What are the loop statements in mysql stored procedures?

MySQL stored procedures provide two loop statements: WHILE and REPEAT: WHILE loop: Repeat the code block according to the condition, and continue execution when the condition is true. REPEAT loop: execute the code block first, then check whether the condition is true, if it is false, execute the code block again.

Loop statements in MySQL stored procedures

MySQL stored procedures support the following two types of loop statements:

WHILE Loop

WHILE loop repeatedly executes a block of code based on specified conditions. The syntax is:

<code class="sql">WHILE condition DO
  -- 代码块
END WHILE;</code>

Among them:

• condition: The condition of the loop. When the condition is true, the code block will continue to execute.
• -- Code block: Code block to be executed repeatedly.

REPEAT Loop

The REPEAT loop first executes the block of code and then checks whether the condition is true. If true, the loop ends; if false, the code block is executed again. The syntax is:

<code class="sql">REPEAT
  -- 代码块
UNTIL condition;</code>

where:

• -- Code block : Code block to be executed repeatedly.
• condition: The condition of the loop. When the condition is true, the loop ends.

Application of loop statements

Loop statements are widely used in stored procedures, including:

• Traverse tables or Array
• Perform repetitive tasks (such as updating or deleting a group of records)
• Simulate complex business processes

Choose appropriate loop statements

When choosing a loop statement, the following factors should be considered:

• Code readability: REPEAT loops are generally considered more readable than WHILE loops.
• Performance: If the condition needs to be checked before each iteration, you should use a WHILE loop; if the condition can be checked at the beginning of the loop, you should use a REPEAT loop.
• Special requirements: WHILE loop allows you to use the BREAK statement to exit the loop at any time within the loop, but REPEAT loop does not.

The above is the detailed content of What are the loop statements in mysql stored procedures?. For more information, please follow other related articles on the PHP Chinese website!