Usage of if else statement in sql

IF-ELSE statement is used in SQL to perform different operations based on conditions. The basic syntax is: If the condition is true, execute statement 1. If the condition is false, statement 2 is executed. The condition is a Boolean expression and the statement can be any valid SQL statement.

Usage of IF-ELSE statement in SQL

IF-ELSE statement is used in SQL to meet certain requirements. Perform different actions when conditions occur. Its basic syntax is as follows:

<code>IF condition THEN statement1
ELSE statement2</code>

Usage instructions:

• ##Condition (condition): Boolean expression to be evaluated.
• Statement 1 (statement1): If the condition is true, the statement to be executed.
• Statement 2 (statement2): If the condition is false, the statement to be executed.

Example:

<code>SELECT CASE
    WHEN age >= 18 THEN '成人'
    ELSE '未成年'
END AS age_group
FROM students;</code>

In this example, the CASE expression uses an IF-ELSE statement to classify a student as "Adult" based on the value of the age column or "minor".

Nested IF-ELSE statements:

IF-ELSE statements can be nested to handle more complex situations. Nested IF-ELSE statements will check subsequent conditions in sequence if the first condition is not met.

<code>IF condition1 THEN statement1
ELSE IF condition2 THEN statement2
ELSE statement3</code>

Tip:

Make sure the conditions are exact and mutually exclusive.
• Each ELSE IF statement must contain an ELSE clause.
• You can also use CASE expressions as an alternative to IF-ELSE statements.

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