选择是否存在其他插入？

Question

IF EXISTS (select * from users where username = 'something') THEN
    select id from users where username = 'something';
ELSE 
    insert into users (username) values ('something');
END IF;

Answer 1

你的陈述很好.唯一的问题是,你不能像普通的查询一样使用它.控制结构类似于IF或WHILE仅允许存储过程或函数.

只需创建一个这样的过程:

delimiter $$

create procedure select_or_insert()
begin

IF EXISTS (select * from users where username = 'something') THEN
    select id from users where username = 'something';
ELSE 
    insert into users (username) values ('something');
END IF;

end $$

并称之为:

call select_or_insert();

而已.