Roshan Thapa

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# HackerRank SQL Problem Solving Questions With Solutions

## 1. Revising the Select Query I | Easy | HackerRank

Query all columns for all American cities in the CITY table with populations larger than 100000. The CountryCode for America is USA.

The CITY table is described as follows:

### Solution

``````SELECT  *  FROM CITY

WHERE COUNTRYCODE='USA'  AND POPULATION >  100000;
``````

## 2. Revising the Select Query II | Easy | HackerRank

Query the NAME field for all American cities in the CITY table with populations larger than 120000. The CountryCode for America is USA.

The CITY table is described as follows:

### Solution

``````SELECT NAME FROM CITY

WHERE COUNTRYCODE ='USA'  AND POPULATION >  120000;
``````

## 3. Select All | Easy | HackerRank

Query all columns (attributes) for every row in the CITY table.

The CITY table is described as follows:

### Solution

``````SELECT  *  FROM CITY;
``````

## 4. Select By ID | Easy | HackerRank

Query all columns for a city in CITY with the ID 1661.

The CITY table is described as follows:

### Solution

``````SELECT  *  FROM CITY WHERE ID =  1661;
``````

## 5. Japanese Cities' Attributes | Easy | HackerRank

Query all attributes of every Japanese city in the CITY table. The COUNTRYCODE for Japan is JPN.

The CITY table is described as follows:

### Solution

``````SELECT  *  FROM CITY

WHERE COUNTRYCODE='JPN';
``````

## 6. Japanese Cities' Names | Easy | HackerRank

Query the names of all the Japanese cities in the CITY table. The COUNTRYCODE for Japan is JPN.

The CITY table is described as follows:

### Solution

``````SELECT NAME FROM CITY

WHERE COUNTRYCODE ='JPN';
``````

## 7. Average Population | Easy | HackerRank

Query the average population for all cities in CITY, rounded down to the nearest integer.

Input Format

The CITY table is described as follows:

### Solution

``````SELECT  ROUND(AVG(POPULATION))

FROM CITY;
``````

## 8. Japan Population | Easy | HackerRank

Query the sum of the populations for all Japanese cities in CITY. The COUNTRYCODE for Japan is JPN.

Input Format

The CITY table is described as follows:

### Solution

``````SELECT  SUM(POPULATION)

FROM CITY

WHERE COUNTRYCODE =  'JPN';
``````

## 9. Revising Aggregations - The Count Function | Easy | HackerRank

Query a count of the number of cities in CITY having a Population larger than 100,000.

Input Format

The CITY table is described as follows:

### Solution

``````SELECT  COUNT(ID)  FROM CITY

WHERE POPULATION >  100000;
``````

## 10. Revising Aggregations - The Sum Function | Easy | HackerRank

Query the total population of all cities in CITY where District is California.

Input Format

The CITY table is described as follows:

### Solution

``````SELECT  SUM(POPULATION)  FROM CITY

WHERE DISTRICT =  'California';
``````

## 11. Revising Aggregations - Averages | Easy | HackerRank

Query the average population of all cities in CITY where District is California.

Input Format

The CITY table is described as follows:

### Solution

``````SELECT  AVG(POPULATION)  FROM CITY

WHERE DISTRICT =  'California';
``````

## 12. Population Density Difference | Easy | HackerRank

Query the difference between the maximum and minimum populations in CITY.

Input Format

The CITY table is described as follows:

### Solution

``````SELECT  MAX(POPULATION)  -  MIN(POPULATION)

FROM CITY;
``````

## 13. African Cities | Easy | HackerRank

Given the CITY and COUNTRY tables, query the names of all cities where the CONTINENT is 'Africa'.

Note: CITY.CountryCode and COUNTRY.Code are matching key columns.

Input Format The CITY and COUNTRY tables are described as follows:

### Solution

``````SELECT ci.Name

FROM CITY ci

JOIN COUNTRY co

ON co.code = ci.countrycode

WHERE CONTINENT ='Africa'
``````

## 14. Asian Population | Easy | HackerRank

Given the CITY and COUNTRY tables, query the sum of the populations of all cities where the CONTINENT is 'Asia'.

Note: CITY.CountryCode and COUNTRY.Code are matching key columns.

Input Format

### Solution

``````SELECT  SUM(ci.POPULATION)

FROM CITY AS ci

JOIN COUNTRY AS co

ON ci.COUNTRYCODE=co.CODE

WHERE co.CONTINENT='Asia';
``````

## 15. Average Population of Each Continent | Easy | HackerRank

Given the CITY and COUNTRY tables, query the names of all the continents (COUNTRY.Continent) and their respective average city populations (CITY.Population) rounded down to the nearest integer.

Note: CITY.CountryCode and COUNTRY.Code are matching key columns.

Input Format The CITY and COUNTRY tables are described as follows:

### Solution

``````SELECT co.continent, FLOOR(AVG(ci.population))

FROM CITY ci

JOIN COUNTRY co

ON co.code = ci.countrycode

GROUP  BY co.continent;
``````

## 16. Weather Observation Station 1 | Easy | HackerRank

Query a list of CITY and STATE from the STATION table. The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

### Solution

``````SELECT CITY, STATE FROM STATION;
``````

## 17. Weather Observation Station 2 | Easy | HackerRank

Query the following two values from the STATION table:

1. The sum of all values in LAT_N rounded to a scale of 2 decimal places.
2. The sum of all values in LONG_W rounded to a scale of 2 decimal places.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

Output Format

Your results must be in the form:

lat lon

where lat is the sum of all values in LAT_N and lon is the sum of all values in LONG_W. Both results must be rounded to a scale of 2 decimal places.

### Solution

``````SELECT  ROUND(SUM(LAT_N),  2),  ROUND(SUM(LONG_W),  2)

FROM STATION;
``````

## 18. Weather Observation Station 3 | Easy | HackerRank

Query a list of CITY names from STATION for cities that have an even ID number. Print the results in any order, but exclude duplicates from the answer. The STATION table is described as follows

where LAT_N is the northern latitude and LONG_W is the western longitude.

### Solution

``````#Solution 1:

SELECT  DISTINCT CITY FROM STATION

WHERE ID %  2  =  0;

#Solution 2:

SELECT  DISTINCT CITY FROM STATION

WHERE  MOD(ID,  2)  =  0;
``````

## 19. Weather Observation Station 4 | Easy | HackerRank

Find the difference between the total number of CITY entries in the table and the number of distinct CITY entries in the table. The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

For example, if there are three records in the table with CITY values 'New York', 'New York', 'Bengalaru', there are 2 different city names: 'New York' and 'Bengalaru'. The query returns 1, because

`total number of records - number of unique city names = 3 - 2 = 1`

### Solution

``````SELECT  COUNT(CITY)-  COUNT(DISTINCT CITY)

FROM STATION;
``````

## 20. Weather Observation Station 5 | Easy | HackerRank

Query the two cities in STATION with the shortest and longest CITY names, as well as their respective lengths (i.e.: number of characters in the name). If there is more than one smallest or largest city, choose the one that comes first when ordered alphabetically. The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

Sample Input

For example, CITY has four entries: DEF, ABC, PQRS and WXY.

Sample Output

ABC 3

PQRS 4

Explanation

When ordered alphabetically, the CITY names are listed as ABC, DEF, PQRS, and WXY, with lengths and . The longest name is PQRS, but there are options for shortest named city. Choose ABC, because it comes first alphabetically.

Note You can write two separate queries to get the desired output. It need not be a single query.

### Solution

``````SELECT CITY, LENGTH(CITY)  FROM STATION ORDER  BY LENGTH(CITY), CITY LIMIT  1;

SELECT CITY, LENGTH(CITY)  FROM STATION ORDER  BY LENGTH(CITY)  DESC, CITY LIMIT  1;
``````

## 21. Weather Observation Station 6 | Easy | HackerRank

Query the list of CITY names starting with vowels (i.e., a, e, i, o, or u) from STATION. Your result cannot contain duplicates.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

# Solution 1:

``````SELECT CITY FROM STATION

WHERE  LEFT(UPPER(CITY),1)  IN  ('A','E','I','O','U');
``````

# Solution 2:

``````SELECT  DISTINCT CITY FROM STATION

WHERE CITY REGEXP  '^[aeiou]';
``````

## 22. Weather Observation Station 7 | Easy | HackerRank

Query the list of CITY names ending with vowels (a, e, i, o, u) from STATION. Your result cannot contain duplicates.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

# Solution 1:

``````SELECT  DISTINCT CITY FROM STATION

WHERE  RIGHT(UPPER(CITY),1)  IN('A','E','I','O','U');
``````

# Solution 2:

``````SELECT  DISTINCT CITY FROM STATION

WHERE CITY REGEXP  '[aeiou]\$';
``````

## 23. Weather Observation Station 8 | Easy | HackerRank

Query the list of CITY names from STATION which have vowels (i.e., a, e, i, o, and u) as both their first and last characters. Your result cannot contain duplicates.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

# Solution 1:

``````SELECT  DISTINCT CITY

FROM STATION

WHERE  LEFT(UPPER(CITY),1)  IN('A','E','I','O','U')  AND

RIGHT(UPPER(CITY),1)  IN('A','E','I','O','U');
``````

# Solution 2:

``````SELECT  DISTINCT CITY FROM STATION

WHERE CITY REGEXP  '^[aeiou].*[aeiou]\$';
``````

## 24. Weather Observation Station 9 | Easy | HackerRank

Query the list of CITY names from STATION that do not start with vowels. Your result cannot contain duplicates.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

# Solution 1:

``````SELECT  DISTINCT CITY

FROM STATION

WHERE  LEFT(UPPER(CITY),1)  NOT  IN('A','E','I','O','U');
``````

# Solution 2:

``````SELECT  DISTINCT CITY FROM STATION

WHERE CITY REGEXP  '^[^aeiou]';
``````

## 25. Weather Observation Station 10 | Easy | HackerRank

Query the list of CITY names from STATION that do not end with vowels. Your result cannot contain duplicates.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

# Solution 1:

``````SELECT  DISTINCT CITY

FROM STATION

WHERE  RIGHT(UPPER(CITY),1)  NOT  IN('A','E','I','O','U');
``````

# Solution 2:

``````SELECT  DISTINCT CITY FROM STATION

WHERE CITY REGEXP  '[^aeiou]\$';
``````

## 26. Weather Observation Station 11 | Easy | HackerRank

Query the list of CITY names from STATION that either do not start with vowels or do not end with vowels. Your result cannot contain duplicates.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

# Solution 1:

``````SELECT  DISTINCT CITY

FROM STATION

WHERE  LEFT(UPPER(CITY),1)  NOT  IN('A','E','I','O','U')

OR  RIGHT(UPPER(CITY),1)  NOT  IN('A','E','I','O','U');
``````

# Solution 2:

``````SELECT  DISTINCT CITY FROM STATION

WHERE CITY REGEXP  '^[^aeiou]|[^aeiou]\$';
``````

## 27. Weather Observation Station 12 | Easy | HackerRank

Query the list of CITY names from STATION that do not start with vowels and do not end with vowels. Your result cannot contain duplicates.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

# Solution 1:

``````SELECT  DISTINCT CITY

FROM STATION

WHERE  LEFT(UPPER(CITY),1)  NOT  IN('A','E','I','O','U')

AND  RIGHT(UPPER(CITY),1)  NOT  IN('A','E','I','O','U');
``````

# Solution 2:

``````SELECT  DISTINCT CITY FROM STATION

WHERE CITY REGEXP  '^[^aeiou].*[^aeiou]\$';
``````

## 28. Weather Observation Station 13 | Easy | HackerRank

Query the sum of Northern Latitudes (LAT_N) from STATION having values greater than 38.7880 and less than 137.2345. Truncate your answer to 4 decimal places.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

### Solution

``````SELECT  ROUND(SUM(LAT_N),4)  AS sum_lat

FROM STATION

WHERE LAT_N >  38.7880  AND LAT_N <  137.2345;
``````

## 29. Weather Observation Station 14 | Easy | HackerRank

Query the greatest value of the Northern Latitudes (LAT_N) from STATION that is less than 137.2345. Truncate your answer to 4 decimal places.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

### Solution

``````SELECT  ROUND(MAX(LAT_N),4)  AS max_lat_n

FROM STATION

WHERE LAT_N <  137.2345;
``````

## 30. Weather Observation Station 15 | Easy | HackerRank

Query the Western Longitude (LONG_W) for the largest Northern Latitude (LAT_N) in STATION that is less than 137.2345. Round your answer to 4 decimal places.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

### Solution

``````SELECT  ROUND(LONG_W,  4)

FROM STATION

WHERE LAT_N <  137.2345

ORDER  BY LAT_N DESC

LIMIT  1;
``````

## 31. Weather Observation Station 16 | Easy | HackerRank

Query the smallest Northern Latitude (LAT_N) from STATION that is greater than 38.7780. Round your answer to 4 decimal places.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

# Solution 1:

``````SELECT  ROUND(MIN(LAT_N),4)

FROM STATION

WHERE LAT_N >  38.7780  ;
``````

# Solution 2:

``````SELECT  ROUND(LAT_N,  4)

FROM STATION

WHERE LAT_N >  38.7780

ORDER  BY LAT_N

LIMIT  1;
``````

## 32. Weather Observation Station 17 | Easy | HackerRank

Query the Western Longitude (LONG_W)where the smallest Northern Latitude (LAT_N) in STATION is greater than 38.7780. Round your answer to 4 decimal places.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

### Solution

``````SELECT  ROUND(LONG_W,  4)

FROM STATION

WHERE LAT_N >  38.7780

ORDER  BY LAT_N

LIMIT  1;
``````

## 33. Weather Observation Station 18 | Medium | HackerRank

Consider P1(a, b) and P2(c, d) to be two points on a 2D plane.

• a happens to equal the minimum value in Northern Latitude (LAT_N in STATION).
• b happens to equal the minimum value in Western Longitude (LONG_W in STATION).
• c happens to equal the maximum value in Northern Latitude (LAT_N in STATION).
• d happens to equal the maximum value in Western Longitude (LONG_W in STATION). Query the Manhattan Distance between points P1 and P2 and round it to a scale of 4 decimal places

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

### Solution

``````SELECT  ROUND((ABS(MIN(LAT_N)-MAX(LAT_N))  + ABS(MIN(LONG_W)-MAX(LONG_W))),4)

FROM STATION;
``````

## 34. Weather Observation Station 19 | Medium | HackerRank

Consider P1(a, c) and P2(b, d) to be two points on a 2D plane where (a, b) are the respective minimum and maximum values of Northern Latitude (LAT_N) and (c, d) are the respective minimum and maximum values of Western Longitude (LONG_W) in STATION.

Query the Euclidean Distance between points P1 and P2 and format your answer to display 4 decimal digits.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

### Solution

``````SELECT  ROUND(SQRT(POW(MIN(LAT_N)-MAX(LAT_N),2)  + POW(MIN(LONG_W)-MAX(LONG_W),2)),4)

FROM STATION;
``````

## 35. Weather Observation Station 20 | Medium | HackerRank

A median is defined as a number separating the higher half of a data set from the lower half. Query the median of the Northern Latitudes (LAT_N) from STATION and round your answer to 4 decimal places.

Input Format

The STATION table is described as follows:

where LAT_N is the northern latitude and LONG_W is the western longitude.

# Solution 1:

``````SELECT  ROUND(S1.LAT_N,  4)

FROM STATION AS S1

WHERE  (SELECT  ROUND(COUNT(S1.ID)/2)  -  1

FROM STATION)  =

(SELECT  COUNT(S2.ID)

FROM STATION AS S2

WHERE S2.LAT_N > S1.LAT_N);
``````

# Solution 2:

``````SELECT  ROUND(MEDIAN(LAT_N),4)

FROM STATION;
``````

## 36. Higher Than 75 Marks | Easy | HackerRank

Query the Name of any student in STUDENTS who scored higher than 75 Marks. Order your output by the last three characters of each name. If two or more students both have names ending in the same last three characters (i.e.: Bobby, Robby, etc.), secondary sort them by ascending ID.

Input Format

The STUDENTS table is described as follows:

The Name column only contains uppercase (A-Z) and lowercase (a-z) letters.

Sample Input

Sample Output

Ashley

Julia

Belvet

Explanation

Only Ashley, Julia, and Belvet have Marks > 75. If you look at the last three characters of each of their names, there are no duplicates and 'ley' < 'lia' < 'vet'.

# Solution 1:

``````SELECT Name

FROM STUDENTS

WHERE MARKS >  75

ORDER  BY  RIGHT(NAME,  3)  ASC, ID;
``````

# Solution 2:

``````SELECT name FROM students

WHERE marks >  75

ORDER  BY SUBSTR(name, LENGTH(name)-2,  3), id;
``````

## 37. Employee Names | Easy | HackerRank

Write a query that prints a list of employee names (i.e.: the name attribute) from the Employee table in alphabetical order.

Input Format

The Employee table containing employee data for a company is described as follows:

where employee_id is an employee's ID number, name is their name, months is the total number of months they've been working for the company, and salary is their monthly salary.

Sample Input

Sample Output

Angela

Bonnie

Frank

Joe

Kimberly

Lisa

Michael

Patrick

Rose

Todd

### Solution

``````SELECT name FROM Employee ORDER  BY name;
``````

## 38. Employee Salaries | Easy | HackerRank

Write a query that prints a list of employee names (i.e.: the name attribute) for employees in Employee having a salary greater than \$2000 per month who have been employees for less than 10 months. Sort your result by ascending employee_id.

Input Format

The Employee table containing employee data for a company is described as follows:

where employee_id is an employee's ID number, name is their name, months is the total number of months they've been working for the company, and salary is the their monthly salary.

Sample Input

Sample Output

Angela

Michael

Todd

Joe

Explanation

Angela has been an employee for 1 month and earns \$3443 per month.

Michael has been an employee for 6 months and earns \$2017 per month.

Todd has been an employee for 5 months and earns \$3396 per month.

Joe has been an employee for 9 months and earns \$3573 per month.

We order our output by ascending employee_id.

### Solution

``````SELECT name

FROM Employee

WHERE salary >  2000  AND months <  10

ORDER  BY employee_id;
``````

## 39. Top Earners | Easy | HackerRank

We define an employee's total earnings to be their monthly salary Ã— months worked, and the maximum total earnings to be the maximum total earnings for any employee in the Employee table. Write a query to find the maximum total earnings for all employees as well as the total number of employees who have maximum total earnings. Then print these values as 2 space-separated integers.

Input Format

The Employee table containing employee data for a company is described as follows:

where employee_id is an employee's ID number, name is their name, months is the total number of months they've been working for the company, and salary is the their monthly salary.

Sample Input

Sample Output

69952 1

Explanation

The table and earnings data is depicted in the following diagram:

The maximum earnings value is 69952. The only employee with earnings = 69952 is Kimberly, so we print the maximum earnings value (69952) and a count of the number of employees who have earned \$69952 (which is 1) as two space-separated values.

### Solution

``````SELECT  (months*salary)  as earnings,  COUNT(*)

FROM Employee

GROUP  BY earnings

ORDER  BY earnings DESC

LIMIT  1;
``````

## 40. The Blunder | Easy | HackerRank

Samantha was tasked with calculating the average monthly salaries for all employees in the EMPLOYEES table, but did not realize her keyboard's 0 key was broken until after completing the calculation. She wants your help finding the difference between her miscalculation (using salaries with any zeros removed), and the actual average salary.

Write a query calculating the amount of error (i.e.: actual - miscalculated average monthly salaries), and round it up to the next integer.

Input Format

The EMPLOYEES table is described as follows:

Note: Salary is per month.

Constraints

1000 < Salary < 105.

Sample Input

Sample Output

2061

Explanation

The table below shows the salaries without zeros as they were entered by Samantha:

Samantha computes an average salary of 98.00. The actual average salary is 2159.00.

The resulting error between the two calculations is 2159.00 - 98.00 = 2061.00. Since it is equal to the integer 2061, it does not get rounded up.

### Solution

``````SELECT CEIL(AVG(Salary)  -  AVG(REPLACE(Salary,  '0',  '')))

FROM EMPLOYEES;
``````

## 41. Type of Triangle | Easy | HackerRank

Write a query identifying the type of each record in the TRIANGLES table using its three side lengths. Output one of the following statements for each record in the table:

• Equilateral: It's a triangle with 3 sides of equal length.
• Isosceles: It's a triangle with 2 sides of equal length.
• Scalene: It's a triangle with 3 sides of differing lengths.
• Not A Triangle: The given values of A, B, and C don't form a triangle.

Input Format

The TRIANGLES table is described as follows:

Each row in the table denotes the lengths of each of a triangle's three sides.

Sample Input

Sample Output

Isosceles

Equilateral

Scalene

Not A Triangle

Explanation

Values in the tuple (20, 20, 23)form an Isosceles triangle, because A â‰¡ B. Values in the tuple (20, 20, 20) form an Equilateral triangle, because A â‰¡ B â‰¡ C. Values in the tuple (20, 21, 22) form a Scalene triangle, because A â‰  B â‰  C. Values in the tuple (13, 14, 30) cannot form a triangle because the combined value of sides A and B is not larger than that of side C.

### Solution

``````SELECT  IF(A+B>C AND A+C>B AND B+C>A,  IF(A=B AND B=C,  'Equilateral',  IF(A=B OR B=C OR A=C,  'Isosceles',  'Scalene')),  'Not A Triangle')

FROM TRIANGLES;
``````

## 42. The PADS | Medium | HackerRank

Generate the following two result sets:

1. Query an alphabetically ordered list of all names in OCCUPATIONS, immediately followed by the first letter of each profession as a parenthetical (i.e.: enclosed in parentheses). For example: AnActorName(A), ADoctorName(D), AProfessorName(P), and ASingerName(S).
2. Query the number of ocurrences of each occupation in OCCUPATIONS. Sort the occurrences in ascending order, and output them in the following format:

`There are a total of [occupation_count] [occupation]s.`

where [occupation_count] is the number of occurrences of an occupation in OCCUPATIONS and [occupation] is the lowercase occupation name. If more than one Occupation has the same [occupation_count], they should be ordered alphabetically.

Note: There will be at least two entries in the table for each type of occupation.

Input Format

The OCCUPATIONS table is described as follows: Occupation will only contain one of the following values: Doctor, Professor, Singer or Actor.

Sample Input

An OCCUPATIONS table that contains the following records:

Sample Output

Ashely(P)

Christeen(P)

Jane(A)

Jenny(D)

Julia(A)

Ketty(P)

Maria(A)

Meera(S)

Priya(S)

Samantha(D)

There are a total of 2 doctors.

There are a total of 2 singers.

There are a total of 3 actors.

There are a total of 3 professors.

Explanation

The results of the first query are formatted to the problem description's specifications. The results of the second query are ascendingly ordered first by number of names corresponding to each profession (2 â‰¤ 2 â‰¤ 3 â‰¤ 3), and then alphabetically by profession (doctor â‰¤ singer, and actor â‰¤ professor).

# Solution 1:

``````SELECT CONCAT(NAME,CONCAT("(",CONCAT(substr(OCCUPATION,1,1),")")))  FROM OCCUPATIONS ORDER  BY NAME ASC;

SELECT  "There are a total of ",  count(OCCUPATION), CONCAT(LOWER(occupation),"s.")  FROM OCCUPATIONS GROUP  BY OCCUPATION ORDER  BY  count(OCCUPATION), OCCUPATION ASC;
``````

# Solution 2:

``````SELECT NAME ||  '('  || SUBSTR(OCCUPATION,  0,  1)  ||  ')'

FROM OCCUPATIONS

ORDER  BY NAME;

SELECT  'There are a total of '  ||  COUNT(*)  ||  ' '  || LOWER(OCCUPATION)  ||  's.'

FROM OCCUPATIONS

GROUP  BY OCCUPATION

ORDER  BY  COUNT(*), OCCUPATION;
``````

## 43. The Report | Medium | HackerRank

You are given two tables: Students and Grades. Students contains three columns ID, Name and Marks.

Ketty gives Eve a task to generate a report containing three columns: Name, Grade and Mark. Ketty doesn't want the NAMES of those students who received a grade lower than 8. The report must be in descending order by grade -- i.e. higher grades are entered first. If there is more than one student with the same grade (8-10) assigned to them, order those particular students by their name alphabetically. Finally, if the grade is lower than 8, use "NULL" as their name and list them by their grades in descending order. If there is more than one student with the same grade (1-7) assigned to them, order those particular students by their marks in ascending order.

Write a query to help Eve.

Sample Input

Sample Output

Maria 10 99

Jane 9 81

Julia 9 88

Scarlet 8 78

NULL 7 63

NULL 7 68

Note

Print "NULL" as the name if the grade is less than 8.

Explanation

Consider the following table with the grades assigned to the students:

So, the following students got 8, 9 or 10 grades:

### Solution

``````SELECT  IF(g.Grade<8,  NULL, s.Name), g.Grade, s.Marks

FROM Students AS s

ON s.Marks

BETWEEN g.Min_Mark AND g.Max_Mark

ORDER  BY g.Grade DESC, s.Name, s.Marks;
``````

## 44. Top Competitors | Medium | HackerRank

Julia just finished conducting a coding contest, and she needs your help assembling the leaderboard! Write a query to print the respective hacker_id and name of hackers who achieved full scores for more than one challenge. Order your output in descending order by the total number of challenges in which the hacker earned a full score. If more than one hacker received full scores in same number of challenges, then sort them by ascending hacker_id.

Input Format

The following tables contain contest data:

• Hackers: The hacker_id is the id of the hacker, and name is the name of the hacker.

• Difficulty: The difficult_level is the level of difficulty of the challenge, and score is the score of the challenge for the difficulty level.

• Challenges: The challenge_id is the id of the challenge, the hacker_id is the id of the hacker who created the challenge, and difficulty_level is the level of difficulty of the challenge.

• Submissions: The submission_id is the id of the submission, hacker_id is the id of the hacker who made the submission, challenge_id is the id of the challenge that the submission belongs to, and score is the score of the submission.

Sample Input

Hackers Table:

Difficulty Table:

Challenges Table:

Submissions Table:

Sample Output

90411 Joe

Explanation

Hacker 86870 got a score of 30 for challenge 71055 with a difficulty level of 2, so 86870 earned a full score for this challenge.

Hacker 90411 got a score of 30 for challenge 71055 with a difficulty level of 2, so 90411 earned a full score for this challenge.

Hacker 90411 got a score of 100 for challenge 66730 with a difficulty level of 6, so 90411 earned a full score for this challenge.

Only hacker 90411 managed to earn a full score for more than one challenge, so we print the their hacker_id and name as 2 space-separated values.

### Solution

``````SELECT h.hacker_id, h.name

FROM Submissions AS s

JOIN Hackers AS h

ON s.hacker_id = h.hacker_id

JOIN Challenges AS c

ON s.challenge_id = c.challenge_id

JOIN Difficulty AS d

ON c.difficulty_level = d.difficulty_level

WHERE s.score = d.score

GROUP  BY h.hacker_id, h.name

HAVING  COUNT(*)>1

ORDER  BY  COUNT(*)  DESC, h.hacker_id;
``````

## 45. Challenges | Medium | HackerRank

Julia asked her students to create some coding challenges. Write a query to print the hacker_id, name, and the total number of challenges created by each student. Sort your results by the total number of challenges in descending order. If more than one student created the same number of challenges, then sort the result by hacker_id. If more than one student created the same number of challenges and the count is less than the maximum number of challenges created, then exclude those students from the result.

Input Format

The following tables contain challenge data:

• Hackers: The hacker_id is the id of the hacker, and name is the name of the hacker.

Sample Input 0

Hackers Table:

Challenges Table:

Sample Output 0

21283 Angela 6

88255 Patrick 5

96196 Lisa 1

Sample Input 1

Hackers Table:

Challenges Table:

Sample Output 1

12299 Rose 6

34856 Angela 6

79345 Frank 4

80491 Patrick 3

81041 Lisa 1

Explanation

For Sample Case 0, we can get the following details:

Students 5077 and 62743 both created 4 challenges, but the maximum number of challenges created is 6 so these students are excluded from the result.

For Sample Case 1, we can get the following details:

Students 12299 and 34856 both created 6 challenges. Because 6 is the maximum number of challenges created, these students are included in the result.

### Solution

``````SELECT c.hacker_id, h.name,  COUNT(c.challenge_id)  AS cnt

FROM Hackers AS h JOIN Challenges AS c ON h.hacker_id = c.hacker_id

GROUP  BY c.hacker_id, h.name HAVING

cnt =  (SELECT  COUNT(c1.challenge_id)  FROM Challenges AS c1 GROUP  BY c1.hacker_id ORDER  BY  COUNT(*)  DESC  LIMIT  1)  OR

cnt NOT  IN  (SELECT  COUNT(c2.challenge_id)  FROM Challenges AS c2 GROUP  BY c2.hacker_id HAVING c2.hacker_id <> c.hacker_id)

ORDER  BY cnt DESC, c.hacker_id;
``````

## 46. Contest Leaderboard | Medium | HackerRank

You did such a great job helping Julia with her last coding contest challenge that she wants you to work on this one, too!

The total score of a hacker is the sum of their maximum scores for all of the challenges. Write a query to print the hacker_id, name, and total score of the hackers ordered by the descending score. If more than one hacker achieved the same total score, then sort the result by ascending hacker_id. Exclude all hackers with a total score of 0 from your result.

Input Format

The following tables contain contest data:

• Hackers: The hacker_id is the id of the hacker, and name is the name of the hacker.

• Submissions: The submission_id is the id of the submission, hacker_id is the id of the hacker who made the submission, challenge_id is the id of the challenge for which the submission belongs to, and score is the score of the submission.

Sample Input

Hackers Table:

Submissions Table:

Sample Output

4071 Rose 191

74842 Lisa 174

84072 Bonnie 100

4806 Angela 89

26071 Frank 85

80305 Kimberly 67

49438 Patrick 43

Explanation

Hacker 4071 submitted solutions for challenges 19797 and 49593, so the total score = 95 + max(43, 96) = 191.

Hacker 74842 submitted solutions for challenges 19797 and 63132, so the total score = max(98, 5) + 76 = 174.

Hacker 84072 submitted solutions for challenges 49593 and 63132, so the total score = 100 + 0 = 100.

The total scores for hackers 4806, 26071, 80305, and 49438 can be similarly calculated.

### Solution

``````SELECT m.hacker_id, h.name,  SUM(m.score)  AS total_score FROM

(SELECT hacker_id, challenge_id,  MAX(score)  AS score FROM Submissions GROUP  BY hacker_id, challenge_id)  AS m

JOIN Hackers AS h ON m.hacker_id = h.hacker_id

GROUP  By m.hacker_id, h.name

HAVING total_score >  0

ORDER  BY total_score DESC, m.hacker_id;
``````

## 47. 15 Days of Learning SQL | Hard | HackerRank

Julia conducted a 15 days of learning SQL contest. The start date of the contest was March 01, 2016 and the end date was March 15, 2016.

Write a query to print total number of unique hackers who made at least 1 submission each day (starting on the first day of the contest), and find the hacker_id and name of the hacker who made maximum number of submissions each day. If more than one such hacker has a maximum number of submissions, print the lowest hacker_id. The query should print this information for each day of the contest, sorted by the date.

Input Format

The following tables hold contest data:

• Hackers: The hacker_id is the id of the hacker, and name is the name of the hacker.

• Submissions: The submission_date is the date of the submission, submission_id is the id of the submission, hacker_id is the id of the hacker who made the submission, and score is the score of the submission.

Sample Input

For the following sample input, assume that the end date of the contest was March 06, 2016.

Hackers Table:

Submissions Table:

Sample Output

2016-03-01 4 20703 Angela

2016-03-02 2 79722 Michael

2016-03-03 2 20703 Angela

2016-03-04 2 20703 Angela

2016-03-05 1 36396 Frank

2016-03-06 1 20703 Angela

Explanation

On March 01, 2016 hackers 20703, 36396, 53473, and 79722 made submissions. There are 4 unique hackers who made at least one submission each day. As each hacker made one submission, 20703 is considered to be the hacker who made maximum number of submissions on this day. The name of the hacker is Angela.

On March 02, 2016 hackers 15758, 20703, and 79722 made submissions. Now 20703 and 79722 were the only ones to submit every day, so there are 2 unique hackers who made at least one submission each day. 79722 made 2 submissions, and name of the hacker is Michael.

On March 03, 2016 hackers 20703, 36396, and 79722 made submissions. Now 20703 and 79722 were the only ones, so there are 2 unique hackers who made at least one submission each day. As each hacker made one submission so 20703 is considered to be the hacker who made maximum number of submissions on this day. The name of the hacker is Angela.

On March 04, 2016 hackers 20703, 44065, 53473, and 79722 made submissions. Now 20703 and 79722 only submitted each day, so there are unique 2 hackers who made at least one submission each day. As each hacker made one submission so 20703 is considered to be the hacker who made maximum number of submissions on this day. The name of the hacker is Angela.

On March 05, 2016 hackers 20703, 36396, 38289 and 62529 made submissions. Now 20703 only submitted each day, so there is only 1 unique hacker who made at least one submission each day. 36396 made 2 submissions and name of the hacker is Frank.

On March 06, 2016 only 20703 made submission, so there is only 1 unique hacker who made at least one submission each day. 20703 made 1 submission and name of the hacker is Angela.

### Solution

``````SELECT SUBMISSION_DATE,

(SELECT  COUNT(DISTINCT HACKER_ID)

FROM SUBMISSIONS S2

WHERE S2.SUBMISSION_DATE = S1.SUBMISSION_DATE AND

(SELECT  COUNT(DISTINCT S3.SUBMISSION_DATE)

FROM SUBMISSIONS S3 WHERE S3.HACKER_ID = S2.HACKER_ID AND S3.SUBMISSION_DATE < S1.SUBMISSION_DATE)  = DATEDIFF(S1.SUBMISSION_DATE ,  '2016-03-01')),

(SELECT HACKER_ID FROM SUBMISSIONS S2 WHERE S2.SUBMISSION_DATE = S1.SUBMISSION_DATE

GROUP  BY HACKER_ID ORDER  BY  COUNT(SUBMISSION_ID)  DESC, HACKER_ID LIMIT  1)  AS TMP,

(SELECT NAME FROM HACKERS WHERE HACKER_ID = TMP)

FROM

(SELECT  DISTINCT SUBMISSION_DATE FROM SUBMISSIONS) S1

GROUP  BY SUBMISSION_DATE;
``````

## 48. Binary Tree Nodes | Medium | HackerRank

You are given a table, BST, containing two columns: N and P, where N represents the value of a node in Binary Tree, and P is the parent of N.

Write a query to find the node type of Binary Tree ordered by the value of the node. Output one of the following for each node:

• Root: If node is root node.
• Leaf: If node is leaf node.
• Inner: If node is neither root nor leaf node.

Sample Input

Sample Output

1 Leaf

2 Inner

3 Leaf

5 Root

6 Leaf

8 Inner

9 Leaf

Explanation

The Binary Tree below illustrates the sample:

# Solution 1:

``````SELECT N,

IF(P IS  NULL,  'Root',  IF((SELECT  COUNT(*)  FROM BST WHERE P=B.N)>0,  'Inner',  'Leaf'))

FROM BST AS B ORDER  BY N;
``````

# Solution 2:

``````SELECT N,

IF(P IS  NULL,  'Root',  IF(B.N IN  (SELECT P FROM BST),  'Inner',  'Leaf'))

FROM BST AS B ORDER  BY N;
``````

## 49. New Companies | Medium | HackerRank

Amber's conglomerate corporation just acquired some new companies. Each of the companies follows this hierarchy:

Given the table schemas below, write a query to print the company_code, founder name, total number of lead managers, total number of senior managers, total number of managers, and total number of employees. Order your output by ascending company_code.

Note:

• The tables may contain duplicate records.
• The company_code is string, so the sorting should not be numeric. For example, if the company_codes are C_1, C_2, and C_10, then the ascending company_codes will be C_1, C_10, and C_2.

Input Format

The following tables contain company data:

• Company: The company_code is the code of the company and founder is the founder of the company.

• Lead_Manager: The lead_manager_code is the code of the lead manager, and the company_code is the code of the working company.

• Senior_Manager: The senior_manager_code is the code of the senior manager, the lead_manager_code is the code of its lead manager, and the company_code is the code of the working company.

• Manager: The manager_code is the code of the manager, the senior_manager_code is the code of its senior manager, the lead_manager_code is the code of its lead manager, and the company_code is the code of the working company.

• Employee: The employee_code is the code of the employee, the manager_code is the code of its manager, the senior_manager_code is the code of its senior manager, the lead_manager_code is the code of its lead manager, and the company_code is the code of the working company.

Sample Input

Company Table:

Senior_Manager Table:

Manager Table:

Employee Table:

Sample Output

C1 Monika 1 2 1 2

C2 Samantha 1 1 2 2

Explanation

In company C1, the only lead manager is LM1. There are two senior managers, SM1 and SM2, under LM1. There is one manager, M1, under senior manager SM1. There are two employees, E1 and E2, under manager M1.

In company C2, the only lead manager is LM2. There is one senior manager, SM3, under LM2. There are two managers, M2 and M3, under senior manager SM3. There is one employee, E3, under manager M2, and another employee, E4, under manager, M3.

# Solution 1:

``````SELECT c.company_code, c.founder,

COUNT(DISTINCT m.manager_code),  COUNT(DISTINCT e.employee_code)

FROM Company c, Lead_Manager l, Senior_Manager s, Manager m, Employee e

WHERE c.company_code = l.company_code AND

s.senior_manager_code = m.senior_manager_code AND

m.manager_code = e.manager_code

GROUP  BY c.company_code, c.founder ORDER  BY c.company_code;
``````

# Solution 2:

``````SELECT c.company_code, c.founder,

COUNT(DISTINCT m.manager_code),  COUNT(DISTINCT e.employee_code)

FROM Company c JOIN Lead_Manager l ON c.company_code = l.company_code JOIN

Manager m ON s.senior_manager_code = m.senior_manager_code JOIN

Employee e ON m.manager_code = e.manager_code

GROUP  BY c.company_code, c.founder ORDER  BY c.company_code;
``````

## 50. Draw The Triangle 1 | Easy | HackerRank

P(R) represents a pattern drawn by Julia in R rows. The following pattern represents P(5):

``````* * * * *
* * * *
* * *
* *
*
``````

Write a query to print the pattern P(20).

# Solution 1:

``````SET  @number  =  21;

SELECT  REPEAT('* ',  @number :=  @number  -  1)

FROM information_schema.tables

LIMIT  20;
``````

# Solution 2:

``````SET  @number  =  21;

SELECT  REPEAT('* ',  @number :=  @number  -  1)

FROM information_schema.tables

WHERE  @number  >  0;
``````

## 51. Draw The Triangle 2 | Easy | HackerRank

P(R) represents a pattern drawn by Julia in R rows. The following pattern represents P(5):

``````*

* *

* * *

* * * *

* * * * *
``````

Write a query to print the pattern P(20).

# Solution 1:

``````SET  @number  =  0;

SELECT  REPEAT('* ',  @number :=  @number+1)

FROM information_schema.tables

LIMIT  20;
``````

# Solution 2:

``````SET  @number  =  0;

SELECT  REPEAT('* ',  @number :=  @number+1)

FROM information_schema.tables

WHERE  @number  <  20;
``````

## 52. Print Prime Numbers | Medium | HackerRank

Write a query to print all prime numbers less than or equal to 1000. Print your result on a single line, and use the ampersand (&) character as your separator (instead of a space).

For example, the output for all prime numbers â‰¤ 10 would be :

2&3&5&7

# Solution 1: MS SQL

``````DECLARE  @table  TABLE  (PrimeNumber INT)

DECLARE  @final  AS  VARCHAR(1500)

SET  @final  =  ''

DECLARE  @counter  INT

SET  @counter  =  2

WHILE  @counter  <=  1000

BEGIN

IF  NOT  EXISTS  (

FROM  @table

WHERE  @counter  % PrimeNumber =  0)

BEGIN

INSERT  INTO  @table  SELECT  @counter

SET  @final  =  @final  + CAST(@counter  AS  VARCHAR(20))+'&'

END

SET  @counter  =  @counter  +  1

END

SELECT SUBSTRING(@final,0,LEN(@final))
``````

# Solution 2:MySQL

``````SELECT GROUP_CONCAT(NUMB SEPARATOR '&')

FROM  (

SELECT  @num:=@num+1  as NUMB FROM

information_schema.tables t1,

information_schema.tables t2,

(SELECT  @num:=1) tmp

) tempNum

WHERE NUMB<=1000  AND  NOT  EXISTS(

SELECT  *  FROM  (

SELECT  @nu:=@nu+1  as NUMA FROM

information_schema.tables t1,

information_schema.tables t2,

(SELECT  @nu:=1) tmp1

LIMIT  1000

) tatata

WHERE FLOOR(NUMB/NUMA)=(NUMB/NUMA)  AND NUMA<NUMB AND NUMA>1

)
``````

## 53. Ollivander's Inventory | Medium | HackerRank

Harry Potter and his friends are at Ollivander's with Ron, finally replacing Charlie's old broken wand.

Hermione decides the best way to choose is by determining the minimum number of gold galleons needed to buy each non-evil wand of high power and age. Write a query to print the id, age, coins_needed, and power of the wands that Ron's interested in, sorted in order of descending power. If more than one wand has same power, sort the result in order of descending age.

Input Format

The following tables contain data on the wands in Ollivander's inventory:

• Wands: The id is the id of the wand, code is the code of the wand, coins_needed is the total number of gold galleons needed to buy the wand, and power denotes the quality of the wand (the higher the power, the better the wand is).

• Wands_Property: The code is the code of the wand, age is the age of the wand, and is_evil denotes whether the wand is good for the dark arts. If the value of is_evil is 0, it means that the wand is not evil. The mapping between code and age is one-one, meaning that if there are two pairs (code1, age1) and (code2, age2), then code1 â‰  code2 and

age1

â‰

age2

Sample Input

Wands Table:

Wands_Property Table:

Sample Output

9 45 1647 10

12 17 9897 10

1 20 3688 8

15 40 6018 7

19 20 7651 6

11 40 7587 5

10 20 504 5

18 40 3312 3

20 17 5689 3

5 45 6020 2

14 40 5408 1

Explanation

The data for wands of age 45 (code 1):

• The minimum number of galleons needed for wand(age = 45, power = 2) = 6020
• The minimum number of galleons needed for wand(age = 45, power = 10) = 1647

The data for wands of age 40 (code 2):

• The minimum number of galleons needed for wand(age = 40, power = 1) = 5408
• The minimum number of galleons needed for wand(age = 40, power = 3) = 3312
• The minimum number of galleons needed for wand(age = 40, power = 5) = 7587
• The minimum number of galleons needed for wand(age = 40, power = 7) = 6018

The data for wands of age 20 (code 4):

• The minimum number of galleons needed for wand(age = 20, power = 5) = 504
• The minimum number of galleons needed for wand(age = 20, power = 6) = 7651
• The minimum number of galleons needed for wand(age = 20, power = 8) = 3688

The data for wands of age 17 (code 5):

• The minimum number of galleons needed for wand(age = 17, power = 3) = 5689
• The minimum number of galleons needed for wand(age = 17, power = 10) = 9897

### Solution

``````SELECT id, age, m.coins_needed, m.power FROM

(SELECT code, power,  MIN(coins_needed)  AS coins_needed FROM Wands GROUP  BY code, power)  AS m

JOIN Wands AS w ON m.code = w.code AND m.power = w.power AND m.coins_needed = w.coins_needed

JOIN Wands_Property AS p ON m.code = p.code

WHERE p.is_evil =  0

ORDER  BY m.power DESC, age DESC;
``````

## 54. Symmetric Pairs | Medium | HackerRank

You are given a table, Functions, containing two columns: X and Y.

Two pairs (X1, Y1) and (X2, Y2) are said to be symmetric pairs if X1 = Y2 and X2 = Y1.

Write a query to output all such symmetric pairs in ascending order by the value of X. List the rows such that X1 â‰¤ Y1.

Sample Input

Sample Output

20 20

20 21

22 23

# Solution 1:

``````SELECT f1.X, f1.Y FROM Functions AS f1

WHERE f1.X = f1.Y AND

(SELECT  COUNT(*)  FROM Functions WHERE X = f1.X AND Y = f1.X)  >  1

UNION

SELECT f1.X, f1.Y FROM Functions AS f1, Functions AS f2

WHERE f1.X <> f1.Y AND f1.X = f2.Y AND f1.Y = f2.X AND f1.X < f2.X

ORDER  BY X;
``````

# Solution 2:

``````SELECT f1.X, f1.Y FROM Functions AS f1

WHERE f1.X = f1.Y AND

(SELECT  COUNT(*)  FROM Functions WHERE X = f1.X AND Y = f1.X)  >  1

UNION

SELECT f1.X, f1.Y FROM Functions AS f1

WHERE f1.X <> f1.Y AND  EXISTS(SELECT X, Y FROM Functions WHERE f1.X = Y AND f1.Y = X AND f1.X < X)

ORDER  BY X;
``````

# Solution 3:

``````SELECT f1.X, f1.Y FROM Functions AS f1

WHERE f1.X = f1.Y AND

(SELECT  COUNT(*)  FROM Functions WHERE X = f1.X AND Y = f1.X)  >  1

UNION

SELECT f1.X, f1.Y FROM Functions AS f1

WHERE  EXISTS(SELECT X, Y FROM Functions WHERE f1.X = Y AND f1.Y = X AND f1.X < X)

ORDER  BY X;
``````

# Solution 4:

``````(SELECT f1.X, f1.Y FROM Functions AS f1

WHERE f1.X = f1.Y GROUP  BY f1.X, f1.Y HAVING  COUNT(*)  >  1)

UNION

(SELECT f1.X, f1.Y FROM Functions AS f1

WHERE  EXISTS(SELECT X, Y FROM Functions WHERE f1.X = Y AND f1.Y = X AND f1.X < X))

ORDER  BY X;
``````

## 55. Interviews | Hard | HackerRank

Samantha interviews many candidates from different colleges using coding challenges and contests. Write a query to print the contest_id, hacker_id, name, and the sums of total_submissions, total_accepted_submissions, total_views, and total_unique_views for each contest sorted by contest_id. Exclude the contest from the result if all four sums are 0.

Note: A specific contest can be used to screen candidates at more than one college, but each college only holds 1 screening contest.

Input Format

The following tables hold interview data:

• Contests: The contest_id is the id of the contest, hacker_id is the id of the hacker who created the contest, and name is the name of the hacker.

• Colleges: The college_id is the id of the college, and contest_id is the id of the contest that Samantha used to screen the candidates.

• Challenges: The challenge_id is the id of the challenge that belongs to one of the contests whose contest_id Samantha forgot, and college_id is the id of the college where the challenge was given to candidates.

• View_Stats: The challenge_id is the id of the challenge, total_views is the number of times the challenge was viewed by candidates, and total_unique_views is the number of times the challenge was viewed by unique candidates.

Contests Table:

Colleges Table:

Challenges Table:

View_Stats Table:

Submission_Stats Table:

Sample Output

66406 17973 Rose 111 39 156 56

66556 79153 Angela 0 0 11 10

94828 80275 Frank 150 38 41 15

Explanation

The contest 66406 is used in the college 11219. In this college 11219, challenges 18765 and 47127 are asked, so from the view and submission stats:

• Sum of total submissions = 27 + 56 + 28 = 111

• Sum of total accepted submissions = 10 + 18 + 11 = 39

• Sum of total views = 43 + 72 + 26 + 15 = 156

• Sum of total unique views = 10 + 13 + 19 + 14 = 56

Similarly, we can find the sums for contests 66556 and 94828.

### Solution

``````SELECT con.contest_id, con.hacker_id, con.name,

SUM(sg.total_submissions),  SUM(sg.total_accepted_submissions),

SUM(vg.total_views),  SUM(vg.total_unique_views)

FROM Contests AS con

JOIN Colleges AS col ON con.contest_id = col.contest_id

JOIN Challenges AS cha ON cha.college_id = col.college_id

LEFT  JOIN

(SELECT ss.challenge_id,  SUM(ss.total_submissions)  AS total_submissions,  SUM(ss.total_accepted_submissions)  AS total_accepted_submissions FROM Submission_Stats AS ss GROUP  BY ss.challenge_id)  AS sg

ON cha.challenge_id = sg.challenge_id

LEFT  JOIN

(SELECT vs.challenge_id,  SUM(vs.total_views)  AS total_views,  SUM(vs.total_unique_views)  AS total_unique_views

FROM View_Stats AS vs GROUP  BY vs.challenge_id)  AS vg

ON cha.challenge_id = vg.challenge_id

GROUP  BY con.contest_id, con.hacker_id, con.name

HAVING  SUM(sg.total_submissions)  +

SUM(sg.total_accepted_submissions)  +

SUM(vg.total_views)  +

SUM(vg.total_unique_views)  >  0

ORDER  BY con.contest_id;
``````

## 56. SQL Project Planning | Medium | HackerRank

You are given a table, Projects, containing three columns: Task_ID, Start_Date and End_Date. It is guaranteed that the difference between the End_Date and the Start_Date is equal to 1 day for each row in the table.

If the End_Date of the tasks are consecutive, then they are part of the same project. Samantha is interested in finding the total number of different projects completed.

Write a query to output the start and end dates of projects listed by the number of days it took to complete the project in ascending order. If there is more than one project that have the same number of completion days, then order by the start date of the project.

Sample Input

Sample Output

2015-10-28 2015-10-29

2015-10-30 2015-10-31

2015-10-13 2015-10-15

2015-10-01 2015-10-04

Explanation

The example describes following four projects:

• Project 1: Tasks 1, 2 and 3 are completed on consecutive days, so these are part of the project. Thus start date of project is 2015-10-01 and end date is 2015-10-04, so it took 3 days to complete the project.
• Project 2: Tasks 4 and 5 are completed on consecutive days, so these are part of the project. Thus, the start date of project is 2015-10-13 and end date is 2015-10-15, so it took 2 days to complete the project.
• Project 3: Only task 6 is part of the project. Thus, the start date of project is 2015-10-28 and end date is 2015-10-29, so it took 1 day to complete the project.
• Project 4: Only task 7 is part of the project. Thus, the start date of project is 2015-10-30 and end date is 2015-10-31, so it took 1 day to complete the project.

### Solution

``````SELECT Start_Date,  MIN(End_Date)  FROM

(SELECT Start_Date FROM Projects WHERE Start_Date NOT  IN  (SELECT End_Date FROM Projects))  AS s,

(SELECT End_Date FROM Projects WHERE End_Date NOT  IN  (SELECT Start_Date FROM Projects))  AS e

WHERE Start_Date < End_Date

GROUP  BY Start_Date

ORDER  BY DATEDIFF(MIN(End_Date), Start_Date), Start_Date;
``````

## 57. Placements | Medium | HackerRank

You are given three tables: Students, Friends and Packages. Students contains two columns: ID and Name. Friends contains two columns: ID and Friend_ID (ID of the ONLY best friend). Packages contains two columns: ID and Salary (offered salary in \$ thousands per month).

Write a query to output the names of those students whose best friends got offered a higher salary than them. Names must be ordered by the salary amount offered to the best friends. It is guaranteed that no two students got same salary offer.

Sample Input

Sample Output

Samantha

Julia

Scarlet

Explanation

See the following table:

Now,

• Samantha's best friend got offered a higher salary than her at 11.55
• Julia's best friend got offered a higher salary than her at 12.12
• Scarlet's best friend got offered a higher salary than her at 15.2
• Ashley's best friend did NOT get offered a higher salary than her

The name output, when ordered by the salary offered to their friends, will be:

• Samantha
• Julia
• Scarlet

### Solution

``````SELECT s.Name FROM Students AS s

JOIN Packages AS sp ON s.ID = sp.ID

JOIN Friends AS f ON s.ID = f.ID

JOIN Packages AS fp ON f.Friend_ID = fp.ID

WHERE sp.Salary < fp.Salary

ORDER  BY fp.Salary;
``````

## 58. Occupations | Medium | HackerRank

Pivot the Occupation column in OCCUPATIONS so that each Name is sorted alphabetically and displayed underneath its corresponding Occupation. The output column headers should be Doctor, Professor, Singer, and Actor, respectively.

Note: Print NULL when there are no more names corresponding to an occupation.

Input Format

The OCCUPATIONS table is described as follows:

Occupation will only contain one of the following values: Doctor, Professor, Singer or Actor.

Sample Input

Sample Output

Jenny Ashley Meera Jane

Samantha Christeen Priya Julia

NULL Ketty NULL Maria

Explanation

The first column is an alphabetically ordered list of Doctor names. The second column is an alphabetically ordered list of Professor names. The third column is an alphabetically ordered list of Singer names. The fourth column is an alphabetically ordered list of Actor names. The empty cell data for columns with less than the maximum number of names per occupation (in this case, the Professor and Actor columns) are filled with NULL values.

### Solution

``````SET  @r1=0,  @r2=0,  @r3  =0,  @r4=0;

SELECT  MIN(Doctor),  MIN(Professor),  MIN(Singer),  MIN(Actor)  FROM

(SELECT  CASE Occupation WHEN  'Doctor'  THEN  @r1:=@r1+1

WHEN  'Professor'  THEN  @r2:=@r2+1

WHEN  'Singer'  THEN  @r3:=@r3+1

WHEN  'Actor'  THEN  @r4:=@r4+1  END

AS RowLine,

CASE  WHEN Occupation =  'Doctor'  THEN Name END  AS Doctor,

CASE  WHEN Occupation =  'Professor'  THEN Name END  AS Professor,

CASE  WHEN Occupation =  'Singer'  THEN Name END  AS Singer,

CASE  WHEN Occupation =  'Actor'  THEN Name END  AS Actor

FROM OCCUPATIONS ORDER  BY Name)  AS t

GROUP  BY RowLine;
``````