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1 definition

Also known as set comparison subquery

Internal query returns multiple rows

Use the multiline comparison operator

2 multiline comparison operator

-- multiple subqueries-- INSELECT employee_id, manager_id, department_id FROM employees WHERE manager_id IN (--look for the same manager_id in the returned set SELECT manager_id FROM employees WHERE employee_id IN (141,147)) -- ANY# question: returns the employee number, name, job_id and salary last_name, job_id, salary job_id! = 'IT_PROG' AND salary of any employee in the job_id whose salary is lower than that of job_id in the' IT_PROG' department.

< ANY ( -- 比任意一个小都可以 SELECT salary FROM employees WHERE job_id = 'IT_PROG' );-- ALL#题目：返回其它job_id中比job_id为'IT_PROG'部门所有工资低的员工的员工号、姓名、job_id 以及salary AND salary < ALL ( -- 比所有的都小才可以3 空值问题3.1 问题 -- 空值问题SELECT last_name FROM employees WHERE employee_id NOT IN ( SELECT -- 子查询中的结果有NULL manager_id employees) 子查询的结果：

Query results:

3.2 Resolution

Just remove the NULL from the subquery

-- Null value problem solving SELECT last_name FROM employees WHERE employee_id NOT IN (SELECT manager_id FROM employees manager_id IS NOT NULL)

Subquery removes NULL:

Query results:

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