How to write judgment statements in sql

SQL judgment statement is used to evaluate conditions and perform corresponding operations. Its syntax is IF condition THEN statement1 [ELSE statement2]. A condition can be a logical expression, a comparison expression, or an expression that returns a Boolean value. If the condition is true, statement1 is executed; if false, statement2 (if provided) is executed. Other judgment statements include the CASE statement (performs an operation based on multiple conditions), the COALESCE function (returns the first non-null value), and the NULLIF function (checks whether two expressions are equal and returns NULL). Decision statements aid in data validation and control flow.

SQL judgment statement

The judgment statement in SQL is used to evaluate data based on given conditions. And perform corresponding operations based on the evaluation results.

Syntax:

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

Where:

• condition: The condition to be evaluated.
• statement1: The statement to be executed if the condition is true.
• statement2 (optional): The statement to be executed if the condition is false.

Usage:

1. Conditional expression: The conditional expression can be a logical expression, a comparison expression or any Other expressions that return a Boolean value.
2. True and false branches: If the condition is true, execute statement1; if the condition is false, execute statement2 (if provided) .

Example:

IF salary > 50000 THEN
  PRINT "高收入"
ELSE
  PRINT "低收入"

Other judgment statements:

ExceptIF-ELSE In addition to statements, there are other judgment statements in SQL:

• CASE statement: is used to perform different operations based on multiple conditions.
• COALESCE function: Used to return the first non-null value.
• NULLIF function: is used to check whether two expressions are equal, and if they are equal, NULL is returned.

Note:

• Judgment statements are very useful for data validation and control flow.
• When writing judgment statements, consider all possible situations to ensure the correctness of the program.
• Judgment statements can be nested to create more complex operations.

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