• Create view语句是指将某个查询数据的定义保留下来，以便随时
调用
• view本身不存储查询结果，只是一个定义
mysql> select * from orders_temp union all select * from orders_temp2; +-----------+---------------------+---------+----+ | order_num | order_date | cust_id | id | +-----------+---------------------+---------+----+ | 20007 | 2005-09-30 00:00:00 | 10004 | 1 | | 20008 | 2005-10-03 00:00:00 | 10005 | 2 | | 20009 | 2005-10-08 00:00:00 | 10001 | 3 | | 20007 | 2005-09-30 00:00:00 | 10004 | 1 | | 20008 | 2005-10-03 00:00:00 | 10005 | 2 | | 20009 | 2005-10-08 00:00:00 | 10001 | 3 | | 0 | 2015-10-08 00:00:00 | 10009 | 0 | +-----------+---------------------+---------+----+ 7 rows in set (0.00 sec) mysql> create view v_order as select * from orders_temp union all select * from orders_temp2; Query OK, 0 rows affected (0.11 sec) mysql> select * from v_order; +-----------+---------------------+---------+----+ | order_num | order_date | cust_id | id | +-----------+---------------------+---------+----+ | 20007 | 2005-09-30 00:00:00 | 10004 | 1 | | 20008 | 2005-10-03 00:00:00 | 10005 | 2 | | 20009 | 2005-10-08 00:00:00 | 10001 | 3 | | 20007 | 2005-09-30 00:00:00 | 10004 | 1 | | 20008 | 2005-10-03 00:00:00 | 10005 | 2 | | 20009 | 2005-10-08 00:00:00 | 10001 | 3 | | 0 | 2015-10-08 00:00:00 | 10009 | 0 | +-----------+---------------------+---------+----+ 7 rows in set (0.00 sec)
Or replace关键词表示当创建的视图已经存在时，执行替换命令
• Select_statement子句则是创建视图的select语句，可以是从表中查询数据，也可以从其他视图中查询数据
• 当视图被创建之后，则其定义就已经固定不会再改变，比如一个视图是由select *创建的，则后续对表增加的字段不会成为视图的一部分，而后续对表删除字段则会导致查询视图失败
• 创建的视图默认情况下是属于当前数据库的，当要创建到另外的数据库时则需要在视图名前面加上数据库名
mysql> show create view v_order; +---------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+ | View | Create View | character_set_client | collation_connection | +---------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+ | v_order | CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`%` SQL SECURITY DEFINER VIEW `v_order` AS select `orders_temp`.`order_num` AS `order_num`,`orders_temp`.`order_date` AS `order_date`,`orders_temp`.`cust_id` AS `cust_id`,`orders_temp`.`id` AS `id` from `orders_temp` union all select `orders_temp2`.`order_num` AS `order_num`,`orders_temp2`.`order_date` AS `order_date`,`orders_temp2`.`cust_id` AS `cust_id`,`orders_temp2`.`id` AS `id` from `orders_temp2` | utf8mb4 | utf8mb4_0900_ai_ci | +---------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+ 1 row in set (0.00 sec) mysql> alter table orders_temp add column order_num2 int(10); Query OK, 0 rows affected (0.30 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> alter table orders_temp2 add column order_num2 int(10); Query OK, 0 rows affected (0.03 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> select * from orders_temp; +-----------+---------------------+---------+----+------------+ | order_num | order_date | cust_id | id | order_num2 | +-----------+---------------------+---------+----+------------+ | 20007 | 2005-09-30 00:00:00 | 10004 | 1 | NULL | | 20008 | 2005-10-03 00:00:00 | 10005 | 2 | NULL | | 20009 | 2005-10-08 00:00:00 | 10001 | 3 | NULL | +-----------+---------------------+---------+----+------------+ 3 rows in set (0.00 sec) mysql> select * from orders_temp2; +-----------+---------------------+---------+----+------------+ | order_num | order_date | cust_id | id | order_num2 | +-----------+---------------------+---------+----+------------+ | 20007 | 2005-09-30 00:00:00 | 10004 | 1 | NULL | | 20008 | 2005-10-03 00:00:00 | 10005 | 2 | NULL | | 20009 | 2005-10-08 00:00:00 | 10001 | 3 | NULL | | 0 | 2015-10-08 00:00:00 | 10009 | 0 | NULL | +-----------+---------------------+---------+----+------------+ 4 rows in set (0.00 sec) mysql> select * from v_order; +-----------+---------------------+---------+----+ | order_num | order_date | cust_id | id | +-----------+---------------------+---------+----+ | 20007 | 2005-09-30 00:00:00 | 10004 | 1 | | 20008 | 2005-10-03 00:00:00 | 10005 | 2 | | 20009 | 2005-10-08 00:00:00 | 10001 | 3 | | 20007 | 2005-09-30 00:00:00 | 10004 | 1 | | 20008 | 2005-10-03 00:00:00 | 10005 | 2 | | 20009 | 2005-10-08 00:00:00 | 10001 | 3 | | 0 | 2015-10-08 00:00:00 | 10009 | 0 | +-----------+---------------------+---------+----+ 7 rows in set (0.00 sec) mysql>
mysql> alter table orders_temp2 drop column order_num; Query OK, 0 rows affected (0.59 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> select * from v_order; ERROR 1356 (HY000): View 'company.v_order' references invalid table(s) or column(s) or function(s) or definer/invoker of view lack rights to use them mysql>
mysql> create view v_prod as select prod_id,prod_price from products order by prod_price; Query OK, 0 rows affected (0.03 sec) mysql> select * from v_prod; +---------+------------+ | prod_id | prod_price | +---------+------------+ | FC | 2.50 | | TNT1 | 2.50 | | FU1 | 3.42 | | SLING | 4.49 | | ANV01 | 5.99 | | OL1 | 8.99 | | ANV02 | 9.99 | | FB | 10.00 | | TNT2 | 10.00 | | DTNTR | 13.00 | | ANV03 | 14.99 | | JP1000 | 35.00 | | SAFE | 50.00 | | JP2000 | 55.00 | +---------+------------+ 14 rows in set (0.00 sec) mysql> select * from v_prod order by prod_price desc; +---------+------------+ | prod_id | prod_price | +---------+------------+ | JP2000 | 55.00 | | SAFE | 50.00 | | JP1000 | 35.00 | | ANV03 | 14.99 | | DTNTR | 13.00 | | FB | 10.00 | | TNT2 | 10.00 | | ANV02 | 9.99 | | OL1 | 8.99 | | ANV01 | 5.99 | | SLING | 4.49 | | FU1 | 3.42 | | FC | 2.50 | | TNT1 | 2.50 | +---------+------------+ 14 rows in set (0.00 sec) mysql>