MySQL Sub-query

The select sentence that appears in other SQL statements. (Nested select in select)

#求出学生的平均年龄
Select AVG (age) from Stu_details;

#查找出大于平均年龄的数据
Mysql> SELECT * from Stu_details where >18.25;

#将平均数的SQL语句作为子查询放入上一条语句中
Mysql> SELECT * from Stu_details where > (select AVG (age) from stu_details);

Example:

# #需求: To find, computer and foreign language students
Select d_id from department where D_name in (' Computer Academy ', ' Foreign Language Institute ')
# # sub-query
SELECT * FROM student where dept_id in (select d_id from department where D_name in (' Computer Academy ', ' Foreign Language Institute '));

MySQL Sub-query