Usage of if statement in sql

SQL IF statement executes different queries based on conditions. The syntax is as follows: IF (condition)statement1ELSEstatement2. Among them, condition is the condition, statement1 is the statement executed when the condition is true, and statement2 is the statement executed when the condition is false. Nested IF statements can handle more complex conditions, and IF statements can be used with other SQL statements.

Usage of IF statement in SQL

SQL IF statement is used to execute different queries based on conditions. The syntax is as follows:

<code class="sql">IF (condition)
  statement1
ELSE
  statement2</code>

where:

• condition is the condition to be tested.
• statement1 is a statement that is executed when the condition is true.
• statement2 is a statement that is executed when the condition is false.

Example:

<code class="sql">SELECT
  CASE
    WHEN age >= 18
    THEN '成年'
    ELSE '未成年'
  END AS age_category
FROM users;</code>

In this example, the IF statement is used to determine the age of each user based on the value of the age column Age category. If age is greater than or equal to 18, returns "adult"; otherwise, returns "minor".

Nested IF statements:

You can use nested IF statements to handle more complex conditions. For example:

<code class="sql">SELECT
  CASE
    WHEN age >= 18
    THEN CASE
      WHEN gender = 'M'
      THEN '成年男性'
      ELSE '成年女性'
    END
    ELSE '未成年'
  END AS age_category
FROM users;</code>

In this nested IF statement, the age category is first determined based on age, and then the specific gender category is determined based on gender.

Note:

• IF statement must contain an ELSE clause.
• The data types of statement 1 and statement 2 must be compatible.
• You can use multiple IF statements to handle complex conditions.
• IF statements can be used with other SQL statements, such as SELECT, UPDATE, and DELETE.

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