The IF keyword in SQL is used to perform different actions based on conditions. The syntax is: IF condition THEN code_block_1 [ELSE code_block_2]. IF statements can check whether a value is empty, compare values for equality, and perform different operations based on conditions.
The meaning of IF in SQL
IF in SQL is a keyword used to specify when a specific condition The code block to be executed when satisfied. It is a control flow statement that allows performing different actions based on conditions in a SQL query.
Grammar
##IF The syntax of the statement is as follows:
<code>IF condition THEN code_block_1 [ELSE code_block_2]</code>Among them:
is the condition to be evaluated.
is the code block to be executed if
condition is true.
(optional) is the code block to execute if
condition is false.
Usage
IF statement can be used in various situations, for example:
Example
The following is a sample query using theIF statement:
<code>SELECT CASE WHEN age >= 18 THEN '成年人' ELSE '未成年人' END FROM person;</code>This query gets the age column from table
person and classifies it as "Adult" based on the conditions person" or "minor".
Note
There must be a
THEN clause in the statement, even if there is no
ELSE clause.
statements can be nested within other
IF statements. The
statement is often used in conjunction with other control flow statements such as
CASE.
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