How is “when” used in MySQL?

In MySQL, “when” is one of the keywords used to create conditional expressions. It can be used in two scenarios:

1. In a SELECT statement, the CASE statement is used to define conditions and their corresponding results using the WHEN keyword. The syntax is as follows:

SELECT column_name,
       CASE
           WHEN condition1 THEN result1
           WHEN condition2 THEN result2
           ...
           ELSE result
       END
FROM table_name;

This syntax is used to return different values in the SELECT query result based on conditions. If condition 1 is met, return result1; if condition 2 is met, return result2; if neither condition is met, return result.

1. Define conditions and corresponding update operations using “when” in the UPDATE statement. The syntax is as follows:

UPDATE table_name
SET column_name = CASE
                     WHEN condition1 THEN result1
                     WHEN condition2 THEN result2
                     ...
                     ELSE result
                 END
WHERE condition;

This syntax is used to update data in a table based on conditions. If condition 1 is met, the value of column_name is set to result1; if condition 2 is met, the value of column_name is set to result2; if neither condition is met, the value of column_name is set to result.

In conclusion, when encountering the “when” keyword in MySQL, it is typically used to define conditional expressions and perform relevant operations based on the conditions.