How to use ifelse statement in sql

In SQL, the IF-ELSE statement is used to perform specific operations based on conditions: IF condition THEN statement1; execute statement1 if condition is true. ELSE statement2; Execute statement2 if condition is false (optional). END IF; Terminates the IF-ELSE statement.

The use of IF-ELSE statement in SQL

The IF-ELSE statement is a SQL control flow statement. It performs a specific action based on a conditional expression. The syntax format is:

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

where:

• condition is a Boolean expression that determines whether to execute the statement in the THEN clause.
• statement1 is the statement to be executed when condition is true. The
• ELSE clause is optional, if condition is false, statement2 is executed.
• END IF; Terminates the IF-ELSE statement.

Usage

The IF-ELSE statement is used to control the execution flow of SQL statements and perform different operations according to different conditions. It can be used to:

• Modify query results based on conditions, for example:

<code>SELECT
  CASE
    WHEN age > 18 THEN '成年人'
    ELSE '未成年人'
  END AS 年龄段
FROM people;</code>

• Perform different update or delete operations based on conditions, for example:

<code>UPDATE students
SET grade = CASE
  WHEN score >= 90 THEN 'A'
  ELSE 'B'
END
WHERE id = 1;</code>

Notes

When using the IF-ELSE statement, you need to pay attention to the following:

• condition The expression must return a boolean value (true or false).
• The statements in the THEN and ELSE clauses must be valid SQL statements.
• When nesting IF-ELSE statements, you must pay attention to the indentation and order of statements.
• IF-ELSE statement can be used in stored procedures, triggers and dynamic SQL statements.

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