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HackerRank SQL Practice ①

Revising the Select Query I

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

The CITY table is described as follows:

Solution

Revising the Select Query II

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

The CITY table is described as follows:

Solution

Select All

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

The CITY table is described as follows:

Solution

Select By ID

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

The CITY table is described as follows:

Solution

Japanese Cities’ Attributes

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

The CITY table is described as follows:

Solution

Japanese Cities’ Names

Query the names of all the Japanese cities in the CITY table. The COUNTRYCODE for Japan is .
The CITY table is described as follows:

Solution

Weather Observation Station 1

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

Weather Observation Station 3

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

OR

WHERE MOD(id, 2) = 0

The MOD() function returns the remainder of a number divided by another number.

Weather Observation Station 4

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

Solution

Weather Observation Station 5

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.

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

Solution

Weather Observation 6

Query the list of CITY names starting with vowels (i.e., , , , , or ) 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

Weather Observation Station 7

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

Weather Observation Station 8

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.

Soultion

Weather Observation Station 9

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

Weather Observation Station 10

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

Weather Observation Station 11

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

Weather Observation Station 12

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

Higher Than 75 Marks

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 (-) and lowercase (-) letters.

Solution

Employee Names

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.

Solution

Employee Salaries

Write a query that prints a list of employee names (i.e.: the name attribute) for employees in Employee having a salary greater than 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.

Solution

Asian Population

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

The CITY and COUNTRY tables are described as follows:

Solution

African Cities

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

Average Population of Each Continent

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

The Report

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

Grades contains the following data:

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.

Note

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

Solution

Top Competitors

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.

Solution

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