Case Statement:

Case Statement is used to provide IF-ELSE functionality in a SQL query to fetch result. We provide multiple conditions and according to condition matches the value will change for that that column value.

Syntax:

SELECT CASE (columnname)
  WHEN value1 THEN result1
  WHEN value2 THEN result2
  ...
  ELSE resultN
  END
FROM tablename;

Example:

SELECT EmpName, CASE EmpName
  WHEN 'Sam' THEN 'Salary * 2'
  WHEN 'Mitchell' THEN 'Salary * 1'
  ELSE 'Salary+1000'
  END
  "RevisedSalary"
 Ctiy
FROM Employee;

Output:

EmpName              RevisedSalary                    City
-------------------------------------------------------------------------
Sam                       30000                      Boston
Shaun                     21000                      Texas
Mitchell                  40000                      Boston
Bucky                     21000                      Boston

In the above example we used CASE with EmpName column. When EmpName is SAM then Salary will get double for that employee, When EmpName is Mitchell then Salary will remain as it is for that employee and for other employees the salary will incremented by 1000.