MariaDB VIEW

MariaDB VIEW

VIEW支持UPDATE,INSERT,DELETE ，但虚拟表只上将操作转移到了真正的表上

示例一：替换复杂的JOIN

(jlive)[crashcourse]>SELECT cust_name, cust_contact, prod_id FROM customers, orders, orderitems WHERE customers.cust_id = orders.cust_id AND orderitems.order_num = orders.order_num;

+----------------+--------------+---------+

| cust_name      | cust_contact | prod_id |

+----------------+--------------+---------+

| Coyote Inc.    | Y Lee        | ANV01   |

| Coyote Inc.    | Y Lee        | ANV02   |

| Coyote Inc.    | Y Lee        | TNT2    |

| Coyote Inc.    | Y Lee        | FB      |

| Wascals        | Jim Jones    | JP2000  |

| Yosemite Place | Y Sam        | TNT2    |

| The Fudds      | E Fudd       | FC      |

| Coyote Inc.    | Y Lee        | FB      |

| Coyote Inc.    | Y Lee        | OL1     |

| Coyote Inc.    | Y Lee        | SLING   |

| Coyote Inc.    | Y Lee        | ANV03   |

+----------------+--------------+---------+

11 rows in set (0.00 sec)

(jlive)[crashcourse]>CREATE VIEW productcustomers AS SELECT cust_name, cust_contact, prod_id FROM customers, orders, orderitems WHERE customers.cust_id = orders.cust_id AND orderitems.order_num = orders.order_num;

Query OK, 0 rows affected (0.00 sec)

(jlive)[crashcourse]>DESC productcustomers;

+--------------+----------+------+-----+---------+-------+

| Field        | Type     | Null | Key | Default | Extra |

+--------------+----------+------+-----+---------+-------+

| cust_name    | char(50) | NO   |     | NULL    |       |

| cust_contact | char(50) | YES  |     | NULL    |       |

| prod_id      | char(10) | NO   |     | NULL    |       |

+--------------+----------+------+-----+---------+-------+

3 rows in set (0.00 sec)

(jlive)[crashcourse]>SELECT cust_name, cust_contact FROM productcustomers WHERE prod_id = 'TNT2';

+----------------+--------------+

| cust_name      | cust_contact |

+----------------+--------------+

| Coyote Inc.    | Y Lee        |

| Yosemite Place | Y Sam        |

+----------------+--------------+

2 rows in set (0.00 sec)

示例二：重新格式化查询到的数据

(jlive)[crashcourse]>SELECT Concat(RTrim(vend_name), ' (', RTrim(vend_country), ')') AS vend_title FROM vendors ORDER BY vend_name;

+-------------------------+

| vend_title              |

+-------------------------+

| ACME (USA)              |

| Anvils R Us (USA)       |

| Furball Inc. (USA)      |

| Jet Set (England)       |

| Jouets Et Ours (France) |

| LT Supplies (USA)       |

+-------------------------+

6 rows in set (0.00 sec)

(jlive)[crashcourse]>CREATE VIEW vendorlocations AS SELECT Concat(RTrim(vend_name), ' (', RTrim(vend_country), ')') AS vend_title FROM vendors ORDER BY vend_name;

Query OK, 0 rows affected (0.00 sec)

(jlive)[crashcourse]>DESC vendorlocations;

+------------+--------------+------+-----+---------+-------+

| Field      | Type         | Null | Key | Default | Extra |

+------------+--------------+------+-----+---------+-------+

| vend_title | varchar(103) | YES  |     | NULL    |       |

+------------+--------------+------+-----+---------+-------+

1 row in set (0.00 sec)

(jlive)[crashcourse]>SELECT * FROM vendorlocations;

+-------------------------+

| vend_title              |

+-------------------------+

| ACME (USA)              |

| Anvils R Us (USA)       |

| Furball Inc. (USA)      |

| Jet Set (England)       |

| Jouets Et Ours (France) |

| LT Supplies (USA)       |

+-------------------------+

 

6 rows in set (0.00 sec)

示例三：过滤不需要的数据

(jlive)[crashcourse]>SELECT cust_id, cust_name, cust_email FROM customers WHERE cust_email IS NOT NULL;

+---------+----------------+---------------------+

| cust_id | cust_name      | cust_email          |

+---------+----------------+---------------------+

|   10001 | Coyote Inc.    | ylee@coyote.com     |

|   10003 | Wascals        | rabbit@wascally.com |

|   10004 | Yosemite Place | sam@yosemite.com    |

+---------+----------------+---------------------+

3 rows in set (0.00 sec)

(jlive)[crashcourse]>CREATE VIEW customeremaillist AS SELECT cust_id, cust_name, cust_email FROM customers WHERE cust_email IS NOT NULL;

Query OK, 0 rows affected (0.00 sec)

(jlive)[crashcourse]>DESC customeremaillist;

+------------+-----------+------+-----+---------+-------+

| Field      | Type      | Null | Key | Default | Extra |

+------------+-----------+------+-----+---------+-------+

| cust_id    | int(11)   | NO   |     | 0       |       |

| cust_name  | char(50)  | NO   |     | NULL    |       |

| cust_email | char(255) | YES  |     | NULL    |       |

+------------+-----------+------+-----+---------+-------+

3 rows in set (0.00 sec)

(jlive)[crashcourse]>SELECT * FROM customeremaillist;

+---------+----------------+---------------------+

| cust_id | cust_name      | cust_email          |

+---------+----------------+---------------------+

|   10001 | Coyote Inc.    | ylee@coyote.com     |

|   10003 | Wascals        | rabbit@wascally.com |

|   10004 | Yosemite Place | sam@yosemite.com    |

+---------+----------------+---------------------+

 

3 rows in set (0.00 sec)

示例四：混杂计算

(jlive)[crashcourse]>SELECT order_num, prod_id, quantity, item_price, quantity*item_price AS expanded_price FROM orderitems;

+-----------+---------+----------+------------+----------------+

| order_num | prod_id | quantity | item_price | expanded_price |

+-----------+---------+----------+------------+----------------+

|     20005 | ANV01   |       10 |       5.99 |          59.90 |

|     20005 | ANV02   |        3 |       9.99 |          29.97 |

|     20005 | TNT2    |        5 |      10.00 |          50.00 |

|     20005 | FB      |        1 |      10.00 |          10.00 |

|     20006 | JP2000  |        1 |      55.00 |          55.00 |

|     20007 | TNT2    |      100 |      10.00 |        1000.00 |

|     20008 | FC      |       50 |       2.50 |         125.00 |

|     20009 | FB      |        1 |      10.00 |          10.00 |

|     20009 | OL1     |        1 |       8.99 |           8.99 |

|     20009 | SLING   |        1 |       4.49 |           4.49 |

|     20009 | ANV03   |        1 |      14.99 |          14.99 |

+-----------+---------+----------+------------+----------------+

 

11 rows in set (0.00 sec)

(jlive)[crashcourse]>CREATE OR REPLACE VIEW orderitemsexpanded AS SELECT order_num, prod_id, quantity, item_price, quantity*item_price AS expanded_price FROM orderitems;

Query OK, 0 rows affected (0.00 sec)

(jlive)[crashcourse]>DESC orderitemsexpanded;

+----------------+---------------+------+-----+---------+-------+

| Field          | Type          | Null | Key | Default | Extra |

+----------------+---------------+------+-----+---------+-------+

| order_num      | int(11)       | NO   |     | NULL    |       |

| prod_id        | char(10)      | NO   |     | NULL    |       |

| quantity       | int(11)       | NO   |     | NULL    |       |

| item_price     | decimal(8,2)  | NO   |     | NULL    |       |

| expanded_price | decimal(18,2) | NO   |     | 0.00    |       |

+----------------+---------------+------+-----+---------+-------+

5 rows in set (0.01 sec)

(jlive)[crashcourse]>SELECT * FROM orderitemsexpanded WHERE order_num = 20005;

+-----------+---------+----------+------------+----------------+

| order_num | prod_id | quantity | item_price | expanded_price |

+-----------+---------+----------+------------+----------------+

|     20005 | ANV01   |       10 |       5.99 |          59.90 |

|     20005 | ANV02   |        3 |       9.99 |          29.97 |

|     20005 | TNT2    |        5 |      10.00 |          50.00 |

|     20005 | FB      |        1 |      10.00 |          10.00 |

+-----------+---------+----------+------------+----------------+

 

4 rows in set (0.00 sec)

删除VIEW

(jlive)[crashcourse]>DROP VIEW vendorlocations;

 

Query OK, 0 rows affected (0.16 sec)