Imran53 / SQL-Mastery-for-Interviews

Level up your SQL skills for interviews! Explore a curated collection of SQL resources, interview questions, answers, PDFs, YouTube channels, websites, and Hackerrank solutions. Get ready to excel in SQL-related interviews with comprehensive learning materials and real-world problem-solving examples.

Important_SQL

Revising the Select Query I

Problem Link: https://www.hackerrank.com/challenges/revising-the-select-query/problem?isFullScreen=true

select *
from city
where population>100000 and countrycode="USA";

Revising the Select Query II

Problem Link: https://www.hackerrank.com/challenges/revising-the-select-query-2/problem?isFullScreen=true

select name from city where population>120000 and countrycode="usa";

Select All

Problem Link: https://www.hackerrank.com/challenges/select-all-sql/problem?isFullScreen=true

select * from city;

Select By ID

Problem Link: https://www.hackerrank.com/challenges/select-by-id/problem?isFullScreen=true

select * from city where id=1661;

Japanese Cities' Attributes

Problem Link: https://www.hackerrank.com/challenges/japanese-cities-attributes/problem?isFullScreen=true

Select *
from city
where countrycode="jpn";

Japanese Cities' Names

Problem Link: https://www.hackerrank.com/challenges/japanese-cities-name/problem?isFullScreen=true

select name
from city
where countrycode="jpn";

Weather Observation Station 1

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-1/problem?isFullScreen=true

select city,state from station;

Weather Observation Station 3

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-3/problem?isFullScreen=true

select distinct city from station where id%2=0

Weather Observation Station 4

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-4/problem?isFullScreen=true

select count(city)-count(distinct city) from station;

Weather Observation Station 5

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-5/problem?isFullScreen=true

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;

Weather Observation Station 6

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-6/problem?isFullScreen=true

select distinct(city) from station where
city like "a%" or
city like "e%" or
city like "i%" or
city like "o%" or
city like "u%";

Weather Observation Station 7

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-7/problem?isFullScreen=true

select distinct(city) from station where
city like "%a" or
city like "%e" or
city like "%i" or
city like "%o" or
city like "%u";

Weather Observation Station 8

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-8/problem?isFullScreen=true

select distinct city from station where
(city like "a%" or city like "e%" or city like "i%" or city like "o%" or city like "u%")
and
(city like "%a" or city like "%e" or city like "%i" or city like "%o" or city like "%u");

Weather Observation Station 9

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-9/problem?isFullScreen=true

select distinct city from station where
city not like "a%" and
city not like "e%" and
city not like "i%" and
city not like "o%" and
city not like "u%";

Weather Observation Station 10

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-10/problem?isFullScreen=true

select distinct city from station where
city not like "%a" and
city not like "%e" and
city not like "%i" and
city not like "%o" and
city not like "%u";

Weather Observation Station 11

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-11/problem?isFullScreen=true

select distinct city from station where (city not like 'a%' and city not like 'e%' and city not like 'i%' and city not like 'o%' and city not like 'u%') or (city not like '%a' and city not like '%e' and city not like '%i' and city not like '%o' and city not like '%u');

Weather Observation Station 12

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-12/problem?isFullScreen=true

select distinct city from station where (city not like 'a%' and city not like 'e%' and city not like 'i%' and city not like 'o%' and city not like 'u%') and (city not like '%a' and city not like '%e' and city not like '%i' and city not like '%o' and city not like '%u');

Higher Than 75 Marks

Problem Link: https://www.hackerrank.com/challenges/more-than-75-marks/problem?isFullScreen=true

select name from students where marks>75 order by right(name,3),id;

Employee Names

Problem Link: https://www.hackerrank.com/challenges/name-of-employees/problem?isFullScreen=true

select name from employee order by name;

Employee Salaries

Problem Link: https://www.hackerrank.com/challenges/salary-of-employees/problem?isFullScreen=true

select name from employee where salary>2000 and months<10 order by employee_id;

Revising Aggregations - The Count Function

Problem Link: https://www.hackerrank.com/challenges/revising-aggregations-the-count-function/problem?isFullScreen=true

select count(*) from city where population>100000;

Revising Aggregations - The Sum Function

Problem Link: https://www.hackerrank.com/challenges/revising-aggregations-sum?isFullScreen=true

select sum(population) from city where district="California";

Revising Aggregations - Averages

Problem Link: https://www.hackerrank.com/challenges/revising-aggregations-the-average-function?isFullScreen=true

select avg(population) from city where district="california";

Average Population

Problem Link: https://www.hackerrank.com/challenges/average-population?isFullScreen=true

select floor(avg(population)) from city;

Japan Population

Problem Link: https://www.hackerrank.com/challenges/japan-population?isFullScreen=true

select sum(population) from city where countrycode="jpn";

Population Density Difference

Problem Link: https://www.hackerrank.com/challenges/population-density-difference?isFullScreen=true

select max(population)-min(population) from city;

The Blunder

Problem Link: https://www.hackerrank.com/challenges/the-blunder?isFullScreen=true

select ceil(avg(salary)-avg(replace(salary,0,''))) from employees;

Top Earners

Problem Link: https://www.hackerrank.com/challenges/earnings-of-employees?isFullScreen=true

select salary*months as earnings, count(*)
from employee
group by earnings
order by earnings desc
limit 1;

Weather Observation Station 2

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-2?isFullScreen=true

select round(sum(lat_n),2),round(sum(long_w),2)
from station;

Weather Observation Station 13

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-13?isFullScreen=true

select round(sum(lat_n),4) from station
where lat_n>38.7880 and lat_n<137.2345;

Weather Observation Station 14

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-14?isFullScreen=true

select round(max(lat_n),4)
from station
where lat_n<137.2345;

Weather Observation Station 15

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-15?isFullScreen=true

select round(long_w,4)
from station
where lat_n=(select max(lat_n) from station where lat_n<137.2345);

Weather Observation Station 16

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-16?isFullScreen=true

select round(min(lat_n),4) from station where lat_n>38.7780;

Weather Observation Station 17

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-17?isFullScreen=true

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

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-18?isFullScreen=true

select round(abs(min(lat_n)-max(lat_n))+abs(min(long_w)-max(long_w)),4) from station;

Weather Observation Station 19

Problem Link: https://www.hackerrank.com/challenges/weather-observation-station-19?isFullScreen=true

select round(sqrt(power(max(lat_n)-min(lat_n),2)+power(max(long_w)-min(long_w),2)),4) from station;

Population Census

Problem Link: https://www.hackerrank.com/challenges/asian-population?isFullScreen=true

select sum(city.population)
from city, country
where city.countrycode = country.code and country.continent= 'asia';

African Cities

Problem Link: https://www.hackerrank.com/challenges/african-cities?isFullScreen=true

select city.name from city,country where city.countrycode = country.code and country.continent='Africa';

Average Population of Each Continent

Problem Link: https://www.hackerrank.com/challenges/average-population-of-each-continent?isFullScreen=true

SELECT Country.Continent, FLOOR(AVG(City.Population))
FROM Country, City 
WHERE Country.Code = City.CountryCode 
GROUP BY Country.Continent ;

Department Highest Salary

Problem Link: https://leetcode.com/problems/department-highest-salary/

select d.name as department,e.name as employee, e.salary 
from department d, employee e
where e.departmentid=d.id
and e.salary=(select max(salary) from employee e1 
             where e1.departmentid=d.id);

Department Top Three Salaries

Problem Link: https://leetcode.com/problems/department-top-three-salaries/

select d.name as Department, e1.name as Employee, e1.salary as Salary
    From Employee as e1  join Department as d
    on e1.departmentId = d.id
    where 3 > (Select count(distinct(e2.salary)) 
            from Employee as e2
            where e2.salary>e1.salary
            and e1.departmentId = e2.departmentId);

Second Highest Salary

Problem Link: https://leetcode.com/problems/second-highest-salary/

SELECT MAX(salary) as SecondHighestSalary
FROM Employee
WHERE salary < (SELECT MAX(salary) FROM Employee);

Dept wise highest salary

Select max(salary), deptNo 
From emp 
Group by deptNo;

Salary decreasing order

Select salary from emp order by salary desc;

2nd highest salary

Select max(Salary) from emp where salary <(select max(salary) from emp);

Top 3 highest salary

Select * from(select distinct salary from emp order by salary desc) where rownum<=3;

3rd highest salary

Select * from(select distinct salary from emp order by salary desc) where rownum<=3
Minus
Select * from(select distinct salary from emp order by salary desc) where rownum<=2;

SQL Aliases

SQL aliases are used to give a table, or a column in a table, a temporary name. Aliases are often used to make column names more readable.

Select customerName as customer, customerId as id
From customerTable;

SQL FULL OUTER JOIN

The FULL OUTER JOIN keyword returns all matching records from both tables whether the other table matches or not. So, if there are rows in "Customers" that do not have matches in "Orders", or if there are rows in "Orders" that do not have matches in "Customers", those rows will be listed as well.

SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
FULL OUTER JOIN Orders ON Customers.CustomerID=Orders.CustomerID
ORDER BY Customers.CustomerName;

link : https://www.w3schools.com/sql/sql_join_full.asp