Conditional judgment statements in sql

There are two common conditional judgment statements in SQL: IF-ELSE statement and CASE statement. The IF-ELSE statement executes different statements depending on whether the condition is true or false, while the CASE statement executes the corresponding statement depending on whether the expression value matches different conditions.

Conditional judgment statement in SQL

Conditional judgment statementis evaluated in SQL Statements that condition and take different actions based on the results. They are widely used in SQL queries and operations to filter data from the database, modify data, or control processes.

Type

There are two commonly used conditional judgment statements in SQL:

• IF-ELSEstatement: Evaluates a condition and executes one statement if the condition is true, otherwise executes another statement.
• CASEStatement: Evaluate a condition and execute the corresponding statement based on different condition values.

Syntax

IF-ELSE statement

IF  THEN  ELSE  END IF;

CASE statement

CASE  WHEN  THEN  WHEN  THEN  ... ELSE  END CASE;

Example

Use the IF-ELSE statement to check if the value is greater than 5

SELECT * FROM table_name WHERE value IF value > 5 THEN 'Greater than 5' ELSE 'Less than or equal to 5' END IF;

Use the CASE statement to check the score range

CASE score WHEN 90 TO 100 THEN '优秀' WHEN 80 TO 89 THEN '良好' WHEN 70 TO 79 THEN '中等' ELSE '不及格' END CASE;

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