(13) Process Control in mysql and 13mysql Process Control

(13) Process Control in mysql and 13mysql Process Control
Overview

In mysql, you can use the if/case/loop/leave/iterate/repeat/while statement to control the process.

If statement

If statement,Similar to if statements in advanced languages (c/c ++/php/java.

if search_condition then    statement_list[elseif search_condition then statement_list]...[else statement_list]end if

Example

if mobile='13911113222' and psw='720717' then    set useridx = 10008888;else if mobile='13911113333' and psw='720717' then    set useridx = 10006666;else    select UserID into useridx from User_ID order by rand() limit 1;end if;

Case statement

Case to implement Branch selection that is more complex than if,Similar to switch statements in advanced languages.

case case_value    when when_value then statement_list    [when when_value then statement_list]...    [else statement_list]end case

Example

case sid    when 2 then        set @x1 = 2;    else        set @x1 = 1;end case

Loop, leave, and iterate statements

# Loop syntax [begin_label:] loopstatement_listend loop [end_label]

Example

set @x=0;set @x2=0;ins:loop    set @x=@x+1;    if @x=10 then        leave ins;    elseif mod(@x,2)=0 then        iterate ins;    end if    set @x2=@x2+1;end loop ins;

In the preceding example, the variable x is added to the loop by 1. When x = 10, the loop is exited. When the modulus of x 2 is not 0, the variable x2 is added with 1.

Repeat statement

The repeat statement is a conditional loop control statement,Similar to do... while statements in advanced languages.

[begin_lable:] repeat    statement_listuntil search_conditionend repeat [end_lable]

Example

set @x=0;repeat    set @x = @x +1;until @x>10 end repeat;

While statement

The while statement is a conditional loop control statement,Similar to the while statement in advanced languages.

[begin_label:] while search_condition do    statement_listend while [end_label]

Example

set @x=10;while @x1<0 do    set @x = @x-1;end while;

For how to use Process Control in stored procedures or functions, refer to the following link:
(9) stored procedures and user-defined functions in mysql