Sub-query (most difficult)

2. The so-called subquery is the embedding of several small queries within a query.
   

3. Grammar:

   Select "Distinct" * | column name "Alias", Column name "Alias" ... | Statistical functions, (
   
   select "DISTINCT" *| column name "Alias", Column name "Alias" ... | Statistical functions
   From data table "alias", Data table "Alias" ...
   "Where condition (s)"
   "Group by Group field, Group field, ..."
   "Having group after filter"
   "Order By Field" Asc|desc ", Field" Asc|desc ",......"
   
   ）
   From data table "alias", Data table "Alias",......,select "DISTINCT" *| column name "Alias", Column name "Alias" ... | Statistical functions
   From data table "Alias", Data table "Alias" ...
   "Where condition (s)"
   "Group by Group field, Group field, ..."
   "Having group after filter"
   "ORDER By Field" Asc|desc ", Field" Asc|desc ",......";
   The Where condition (s) (select "DISTINCT" *| column name "Alias", Column name "Alias" ... | Statistical functions
   From data table "Alias", Data table "Alias" ...
   "Where condition (s)"
   "Group by Group field, Group field, ..."
   "Having group after filter"
   "ORDER By Field" Asc|desc ", Field" Asc|desc ",......"）】
   "Group by Group field, Group field, ..."
   "Having a group after filtering,select "DISTINCT" *| column name "Alias", Column name "Alias" ... | Statistical functions
   From data table "Alias", Data table "Alias" ...
   "Where condition (s)"
   "Group by Group field, Group field, ..."
   "Having group after filter"
   "ORDER By Field" Asc|desc ", Field" Asc|desc ",......"】
   "Order By Field" Asc|desc ", Field" Asc|desc ",......"
   

5. The subquery returns a single-row column: Having, where

   The subquery returns a multiple-row column: where

   Subquery returns multiple rows and columns: from

7. Subqueries can also appear in the SELECT clause, but this is rarely done in general. At the same time, the subquery must have "()"when it appears.

9. Use a subquery in the WHERE clause.

   
   

This article is from the "10281302" blog, please be sure to keep this source http://10291302.blog.51cto.com/10281302/1691431

Sub-query (most difficult)