MySQL - subquery - column subquery (multi row subquery)

Column query ( Multi line sub query )

The sub query returns data with multiple rows and single column , It's a list of data . Multi row subqueries are also called set comparison subqueries

When using multi row subqueries, you need to use multi row comparison operators ：

The operator	meaning
IN	Equal to any one of the list , Found in a set is established ,IN and =ANY It's the same
ANY	It needs to be used with the single line comparison operator (>、<、=、<>...), Compare with any value in the sub query results , Once established, it will be established
ALL	It needs to be used with the single line comparison operator (>、<、=、<>...), Compare with all the values returned by the subquery , Only when all conditions are established at the same time
SOME	It's actually ANY Another name for , The functions and ANY identical , So we use ANY

IN The operator

MySQL --- Database query - Conditions of the query IN Use

MySQL --- Multi-table query - Cartesian product and correct multi table query 、 Equivalent connection and unequal connection 、 Internal and external connections ON Generally speaking, it is related to JOIN Use it together

MySQL --- Multi-table query - Seven kinds JOINS Realization 、 Set operations 、 Multi table query exercise

IN Operator is used to determine whether the value of the expression is in the given list ; If it is , The return value is 1, Otherwise, the return value is 0.

NOT IN Function and IN On the contrary ,NOT IN Used to determine whether the value of the expression does not exist in the given list ; If not , The return value is 1, Otherwise, the return value is 0.

• Find out the employee information with the same minimum wage in each department

  • Group by Department , Count the minimum wage of each department

  • Find out the employee information according to the minimum wage

 

Report errors , The subquery returns at most one row , But the requirements need to realize multiple lines , You need to equal 5000 Of 、 be equal to 800 Of 、 be equal to 950 Of 、 be equal to 1300 Salary output

Use IN The operator , When the salary is in this set , Output the corresponding employees

--  Find out the information of each employee 
-- SELECT * FROM emp WHERE sal=();
--  After getting the minimum wage of the whole department, group by department number 
SELECT MIN(sal) FROM emp GROUP BY deptno;
--  Find out the employee information with the same minimum wage in each department 
SELECT * FROM emp WHERE sal IN(SELECT MIN(sal) FROM emp GROUP BY deptno);

Number the Department NULL Remove the employee information of

--  Find out the information of each employee 
-- SELECT * FROM emp WHERE sal=();
--  After getting the minimum wage of the whole department, group by department number 
SELECT MIN(sal) FROM emp GROUP BY deptno;
--  Find out the employee information with the same minimum wage in each department 
SELECT * FROM emp WHERE sal IN(SELECT MIN(sal) FROM emp GROUP BY deptno HAVING deptno IS NOT NULL);

Find out the employee information that is not the same as the minimum wage in each department  

SELECT * FROM emp WHERE sal NOT IN(SELECT MIN(sal) FROM emp GROUP BY deptno HAVING deptno IS NOT NULL);

ANY The operator

ANY The keyword is a MySQL Operator , If the sub query criteria ANY Compared to TRUE, Then it will return Boolean value TRUE

• Query employee information whose salary is higher than any management salary

  • Find out the salary of each management

  • Compare the salary of each employee with that of each manager

--  Find out the information of each employee 
-- SELECT * FROM emp WHERE sal=();
--  Get all the management salaries 
SELECT sal FROM emp WHERE job='MANAGER';
--  Query the information of employees whose salary is higher than any management salary 

Report errors , The subquery should return at most one row , Use at most one value for comparison , A value cannot be compared with multiple values , I don't know whether it's with 2975 Compare 、 Or with 2850 Compare 、 Or with 2450 Compare

--  Find out the information of each employee 
-- SELECT * FROM emp WHERE sal=();
SELECT sal FROM emp WHERE job='MANAGER';
--  Query the information of employees whose salary is higher than any management salary 
SELECT * FROM emp WHERE sal>=ANY(SELECT sal FROM emp WHERE job='MANAGER');

ALL The operator

ALL The keyword is a MySQL Operator , If the sub query criteria ALL Compared to TRUE, Then it will Returns a Boolean value TRUE

• The case is the same as ANY The operator

There is no employee whose salary is equal to 2975、 be equal to 2850、 be equal to 2450

--  Find out the information of each employee 
-- SELECT * FROM emp WHERE sal=();
SELECT sal FROM emp WHERE job='MANAGER';
--  Query the information of all employees whose salary is equal to the management salary  
SELECT * FROM emp WHERE sal=ALL(SELECT sal FROM emp WHERE job='MANAGER');

summary

IN            Judge whether it is in the set , Return true in the set , Do not return false in the set

ANY         Judge whether it is in the set ( and IN equally )

＞ANY     Greater than the smallest one in the set

＜ANY     Less than the one with the largest value in the set

＜＞ANY Not equal to any one in the set

= ALL      Equal to every value in the set

＞ ALL     Larger than the largest value in the set

＜ ALL     Smaller than the smallest value in the set

＜＞ ALL Not equal to every value in the set