A subquery is a SQL query nested inside a larger query.
- A subquery may occur in:
- - A SELECT clause
- - A FROM clause
- - A WHERE clause
- In MySQL subquery can be nested inside a SELECT, INSERT, UPDATE, DELETE, SET, or DO statement or inside another subquery.
- A subquery is usually added within the WHERE Clause of another SQL SELECT statement.
- You can use the comparison operators, such as >, <, or =. The comparison operator can also be a multiple-row operator, such as IN, ANY, SOME, or ALL.
- A subquery can be treated as an inner query, which is a SQL query placed as a part of another query called as outer query.
- The inner query executes first before its parent query so that the results of the inner query can be passed to the outer query.
inner join
It returns the same result set however with this syntax you don’t have to use the table aliases.
Notice that for INNER JOIN clause, the condition in the ON clause is equivalent to the condition in the WHERE clause.
sql having
https://blog.csdn.net/u014401141/article/details/53010608
MySQL子查询
https://www.yiibai.com/mysql/subquery.html
http://www.mysqltutorial.org/mysql-subquery/
inner join
http://www.mysqltutorial.org/mysql-inner-join.aspx
Mysql tutorial