MySQL Tutorial: Subquery Example Detailed Explanation

1. What is a subquery?

When one query is part of another query, we call the inner query a subquery and the outer query the main query.

2. Where can subqueries appear?

   select
       ..(select).
   from
       ..(select).
   where
       ..(select).

As can be seen from the above, subqueries often appear in three places: select can be followed by a subquery; from can be followed by a subquery; where can be followed by a subquery; we refer to them here as: select子查詢, from子查詢, where子查詢.

3. Where subquery

Exercise: Find information about employees who earn above the average salary.

4. Use a subquery after from. (Too important)

Exercise 1: Find the salary grade for the average salary in each department.

The results are as follows:

Exercise 2: Find the average salary level for each employee

The results are as follows:

Note: There are few scenarios where subqueries are used after select, so they will not be described here. If you feel it is necessary, you can go and check it out yourself.

The above is the detailed content of the MySQL tutorial subquery example. For more information about MySQL subqueries, please pay attention to other related articles on 123WORDPRESS.COM!