mysql exists子查询

exists后面的子查询,exists 只关心有没有，返回布尔类型

#案例：查询有员工的部门名

    SELECT department_name FROM departments d WHERE EXISTS(     SELECT *     FROM employees e     WHERE d.`department_id`=e.`department_id` );

或

SELECT department_name FROM departments WHERE department_id IN(     SELECT department_id     FROM employees );

#查询没有女朋友的男神信息

SELECT bo.* FROM boys bo WHERE  NOT EXISTS(     SELECT b.boyfriend_id     FROM beauty b     WHERE b.`boyfriend_id`=bo.`id` );

或

SELECT bo.* FROM boys bo WHERE bo.`id` NOT IN(     SELECT boyfriend_id     FROM beauty b );

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来源：51CTO

作者：wx5d21d5e6e5ab1

链接：https://blog.51cto.com/14437184/2438533