Operation of the strap of a database query - insert sub-query results, modify the query statement to the tape, the tape delete statement query

Inserts results

Statement format

 INSERT 
 INTO <表名>  [(<属性列1> [,<属性列2>…  )]
 子查询;

[Requirements] sub-query
SELECT clause, target columns must match the INTO clause, including

• The number of values
• The type of value

Example: For each department, find the average age of the students, and the results stored in the database

 INSERT
 INTO  Dept_age(Sdept,Avg_age)
 SELECT  Sdept,AVG(Sage) FROM  Student GROUP BY Sdept;

Strap query modification statements

Statement format

 UPDATE  <表名>
 SET  <列名>=<表达式>[,<列名>=<表达式>]…
 WHERE <条件> IN 子查询;

Example: Department of Computer Science all students grades zero

UPDATE SC
SET Grade=0
WHERE Sno  IN ( SELETE Sno FROM Student WHERE Sdept= 'CS' );

Strap query delete statement

Statement format

DELETE FROM <表名>
WHERE <条件> IN 子查询;

Example: Department of Computer Science student enrollment delete all records

DELETE FROM  SC
WHERE  Sno  IN (SELETE  Sno FROM   Student WHERE  Sdept= 'CS') ;