《MySQL必知必会》学习之 第15章 联结表
–机会是留给有准备的人。加油加油。你也不希望机会降临之时，你啥也不会，没有用武之地吧。机会来临之时，就是你才华的舞台。
– 你也不希望你做的是打杂没技术含量的工作吧。
2020-06-16
联结表
创建联结
#wehere子句联结
mysql> select vend_name,prod_name,prod_price from vendors,products
-> where vendors.vend_id=products.vend_id
-> order by vend_name,prod_name;
笛卡尔积
#笛卡尔积
/*
由没有联结条件的表关系返回的结果为笛卡尔积。
检索出的行的数目将是第一个表中的行数乘以第二个表的行数
以下是例子
*/
#删除where联结条件
#返回数据用了供应商vend_name匹配了每个产品prod_name,它包括了供应商不正确的产品
mysql> select vend_name,prod_name,prod_price from vendors,products
>order by vend_name,prod_name;
+----------------+----------------+------------+
| vend_name | prod_name | prod_price |
+----------------+----------------+------------+
| ACME | .5 ton anvil | 5.99 |
| ACME | 1 ton anvil | 9.99 |
| ACME | 2 ton anvil | 14.99 |
| ACME | Bird seed | 10.00 |
| ACME | Carrots | 2.50 |
| ACME | Detonator | 13.00 |
| ACME | Fuses | 3.42 |
| ACME | JetPack 1000 | 35.00 |
| ACME | JetPack 2000 | 55.00 |
| ACME | Oil can | 8.99 |
| ACME | Safe | 50.00 |
| ACME | Sling | 4.49 |
| ACME | TNT (1 stick) | 2.50 |
| ACME | TNT (5 sticks) | 10.00 |
| Anvils R Us | .5 ton anvil | 5.99 |
| Anvils R Us | 1 ton anvil | 9.99 |
| Anvils R Us | 2 ton anvil | 14.99 |
| Anvils R Us | Bird seed | 10.00 |
| Anvils R Us | Carrots | 2.50 |
| Anvils R Us | Detonator | 13.00 |
| Anvils R Us | Fuses | 3.42 |
| Anvils R Us | JetPack 1000 | 35.00 |
| Anvils R Us | JetPack 2000 | 55.00 |
| Anvils R Us | Oil can | 8.99 |
| Anvils R Us | Safe | 50.00 |
| Anvils R Us | Sling | 4.49 |
| Anvils R Us | TNT (1 stick) | 2.50 |
| Anvils R Us | TNT (5 sticks) | 10.00 |
| Furball Inc. | .5 ton anvil | 5.99 |
| Furball Inc. | 1 ton anvil | 9.99 |
| Furball Inc. | 2 ton anvil | 14.99 |
| Furball Inc. | Bird seed | 10.00 |
| Furball Inc. | Carrots | 2.50 |
| Furball Inc. | Detonator | 13.00 |
| Furball Inc. | Fuses | 3.42 |
| Furball Inc. | JetPack 1000 | 35.00 |
| Furball Inc. | JetPack 2000 | 55.00 |
| Furball Inc. | Oil can | 8.99 |
| Furball Inc. | Safe | 50.00 |
| Furball Inc. | Sling | 4.49 |
| Furball Inc. | TNT (1 stick) | 2.50 |
| Furball Inc. | TNT (5 sticks) | 10.00 |
| Jet Set | .5 ton anvil | 5.99 |
| Jet Set | 1 ton anvil | 9.99 |
| Jet Set | 2 ton anvil | 14.99 |
| Jet Set | Bird seed | 10.00 |
| Jet Set | Carrots | 2.50 |
| Jet Set | Detonator | 13.00 |
| Jet Set | Fuses | 3.42 |
| Jet Set | JetPack 1000 | 35.00 |
| Jet Set | JetPack 2000 | 55.00 |
| Jet Set | Oil can | 8.99 |
| Jet Set | Safe | 50.00 |
| Jet Set | Sling | 4.49 |
| Jet Set | TNT (1 stick) | 2.50 |
| Jet Set | TNT (5 sticks) | 10.00 |
| Jouets Et Ours | .5 ton anvil | 5.99 |
| Jouets Et Ours | 1 ton anvil | 9.99 |
| Jouets Et Ours | 2 ton anvil | 14.99 |
| Jouets Et Ours | Bird seed | 10.00 |
| Jouets Et Ours | Carrots | 2.50 |
| Jouets Et Ours | Detonator | 13.00 |
| Jouets Et Ours | Fuses | 3.42 |
| Jouets Et Ours | JetPack 1000 | 35.00 |
| Jouets Et Ours | JetPack 2000 | 55.00 |
| Jouets Et Ours | Oil can | 8.99 |
| Jouets Et Ours | Safe | 50.00 |
| Jouets Et Ours | Sling | 4.49 |
| Jouets Et Ours | TNT (1 stick) | 2.50 |
| Jouets Et Ours | TNT (5 sticks) | 10.00 |
| LT Supplies | .5 ton anvil | 5.99 |
| LT Supplies | 1 ton anvil | 9.99 |
| LT Supplies | 2 ton anvil | 14.99 |
| LT Supplies | Bird seed | 10.00 |
| LT Supplies | Carrots | 2.50 |
| LT Supplies | Detonator | 13.00 |
| LT Supplies | Fuses | 3.42 |
| LT Supplies | JetPack 1000 | 35.00 |
| LT Supplies | JetPack 2000 | 55.00 |
| LT Supplies | Oil can | 8.99 |
| LT Supplies | Safe | 50.00 |
| LT Supplies | Sling | 4.49 |
| LT Supplies | TNT (1 stick) | 2.50 |
| LT Supplies | TNT (5 sticks) | 10.00 |
+----------------+----------------+------------+
84 rows in set (0.05 sec)
内部联结 inner join
#内联结 innner join
#表间相等测试
mysql> select vend_name,prod_name,prod_price from vendors
-> inner join products
-> on vendors.vend_id=products.vend_id;
+-------------+----------------+------------+
| vend_name | prod_name | prod_price |
+-------------+----------------+------------+
| Anvils R Us | .5 ton anvil | 5.99 |
| Anvils R Us | 1 ton anvil | 9.99 |
| Anvils R Us | 2 ton anvil | 14.99 |
| LT Supplies | Fuses | 3.42 |
| LT Supplies | Oil can | 8.99 |
| ACME | Detonator | 13.00 |
| ACME | Bird seed | 10.00 |
| ACME | Carrots | 2.50 |
| ACME | Safe | 50.00 |
| ACME | Sling | 4.49 |
| ACME | TNT (1 stick) | 2.50 |
| ACME | TNT (5 sticks) | 10.00 |
| Jet Set | JetPack 1000 | 35.00 |
| Jet Set | JetPack 2000 | 55.00 |
+-------------+----------------+------------+
14 rows in set (0.03 sec)
#编号为20005的订单中的物品及对应情况;
mysql> select prod_name,vend_name,prod_price,quantity
-> from orderitems,products,vendors
-> where products.vend_id=vendors.vend_id
-> and orderitems.prod_id=products.prod_id
-> and order_num=20005;
+----------------+-------------+------------+----------+
| prod_name | vend_name | prod_price | quantity |
+----------------+-------------+------------+----------+
| .5 ton anvil | Anvils R Us | 5.99 | 10 |
| 1 ton anvil | Anvils R Us | 9.99 | 3 |
| TNT (5 sticks) | ACME | 10.00 | 5 |
| Bird seed | ACME | 10.00 | 1 |
+----------------+-------------+------------+----------+
4 rows in set (0.02 sec)
mysql> #订购产品TNT2的客户列表
-> select cust_name,cust_contact
-> from customers,orders,orderitems
-> where customers.cust_id=orders.cust_id
-> and orders.order_num=orderitems.order_num
-> and prod_id='TNT2';
+----------------+--------------+
| cust_name | cust_contact |
+----------------+--------------+
| Coyote Inc. | Y Lee |
| Yosemite Place | Y Sam |
+----------------+--------------+
2 rows in set (0.01 sec)