HackerRank SQL Practice ③

Aggregation

Revising Aggregations — The Count Function

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(name) 
FROM city 
WHERE population > 100000

Revising Aggregations — Average

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"

Revising Aggregations — The Sum Function

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"

Average Population

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

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 FLOOR(AVG(population)) 
FROM city

Japan Population

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"

Population Density Difference

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

The Blunder

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 zeroes 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 measured in dollars per month and its value is < 10⁵.

Solution

SELECT CEIL(AVG(salary) - AVG(REPLACE(salary, '0', ''))) 
FROM employees

Top Earners

We define an employee’s total earnings to be their monthly salary × 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.

Solution

SELECT (salary * months) a, COUNT(*) 
FROM employee 
GROUP BY a 
ORDER BY a DESC 
LIMIT 1

Weather Observation Station 2

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

Weather Observation Station 13

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 decimal 4 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 TRUNCATE(SUM(lat_n), 4) 
FROM station 
WHERE lat_n > 38.7880 AND lat_n < 137.2345

Weather Observation Station 14

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 TRUNCATE(MAX(lat_n),4) 
FROM station 
WHERE lat_n < 137.2345

Weather Observation Station 15

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

Weather Observation Station 16

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

SELECT ROUND(MIN(lat_n), 4) 
FROM station 
WHERE lat_n > 38.7780

Weather Observation Station 17

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 = (SELECT MIN(lat_n) FROM station WHERE lat_n > 38.7780)

Weather Observation Station 18

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

• happens to equal the minimum value in Northern Latitude (LAT_N in STATION).
• happens to equal the minimum value in Western Longitude (LONG_W in STATION).
• happens to equal the maximum value in Northern Latitude (LAT_N in STATION).
• 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((MAX(lat_n) - MIN(lat_n)) + (MAX(long_w) - MIN(long_w)), 4) 
FROM station

Weather Observation Station 19

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(POWER((MAX(lat_n) - MIN(lat_n)),2) + POWER((MAX(long_W) - MIN(long_w)),2)), 4) 
FROM station