如果在SQL脚本中为有条件的Mysql [英] If conditional in SQL Script for Mysql

问题描述

在执行顺序执行的sql脚本中，是否有一种方法可以引入IF THEN ELSE条件来控制查询执行的流程？

In a sql script that does sequential execution, is there a way one can introduce an IF THEN ELSE conditional to control the flow of query execution?

进入此 http ：//www.bennadel.com/blog/1340-MySQL-Does-Not-Support-IF-ELSE-Statements-In-General-SQL-Work-Flow.htm
表示

I happened to run into this http://www.bennadel.com/blog/1340-MySQL-Does-Not-Support-IF-ELSE-Statements-In-General-SQL-Work-Flow.htm which says that the IF THEN ELSE will not work in a sql script.

还有另外一种方法？

基本上，我想要运行特定的select colName from table命令，并检查colName是否对应于特定值。如果是，继续脚本的其余部分。否则，暂停执行。

Basically, I want to run a particular "select colName from table" command and check if colName corresponds to a particular value. If it does, proceed with the rest of the script. Else, halt execution.

请指教。

推荐答案

在一个过程中包装我的SQL脚本，其中允许条件代码。如果你不想留下声明，你可以在完成后删除该程序。例如：

I just wrap my SQL script in a procedure, where conditional code is allowed. If you'd rather not leave the statements lying around, you can drop the procedure when you're done. Here's an example:

delimiter //

create procedure insert_games() 

begin

    set @platform_id := (select id from platform where name = 'Nintendo DS');

    -- Only insert rows if the platform was found
    if @platform_id is not null then 

        insert into game(name, platform_id) values('New Super Mario Bros', @platform_id);
        insert into game(name, platform_id) values('Mario Kart DS', @platform_id);

    end if;

end;

//

delimiter ;

-- Execute the procedure
call insert_games();

-- Drop the procedure
drop procedure insert_games;

如果没有使用过程，delimiter关键字可能需要一些解释。第一行将定界符切换为//，以便我们可以在我们的过程定义中包含分号，而MySQL尝试解释它们。一旦创建过程，我们将分隔符切换回;所以我们可以照常执行语句。

If you haven't used procedures, the "delimiter" keyword might need some explanation. The first line switches the delimiter to "//" so that we can include semi-colons in our procedure definition without MySQL attempting to interpret them yet. Once the procedure has been created, we switch the delimiter back to ";" so we can execute statements as usual.

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