MySQL subquery and connection operation notes

There is a connection operation between the SQL statements, which must be used in some complex data operations. Simply put, the result of an SQL statement can be part of a connected SQL operation. SQL Structured query statements, subqueries refer to all SQL operations, not a single SELECT statement.

1. Generated by comparison operators:

SELECT user_name,user_idfromWHERE>=(SELECTROUND( AVG (age),0 from users);

You can use Any,some,all to make queries.

SELECT user_name,user_idfromWHERE>= any (SELECT  ROUND(AVG(age),0 from users);

2. Generated by [NOT] In/exis

　　

SELECT user_name,user_idfromWHERE>= not in (SELECT  ROUND(AVG(age),0 from users);

　　

3. By insert ... Select generates

 create  table   Tdb_goods_brands (brand_id  smallint  UNSIGNED primary   Auto_increment, brand_name  varchar  (40 ) not  null  )  select  brand_name from  tdb_ Goods group  by  brand_name 

UPDATE tdb_goods  INNERJOINon=SET= brand_id;

MySQL subquery and connection operation notes