MariaDB Subquery

MariaDB Subquery

prod_id ==> order_num

(jlive)[crashcourse]>SELECT order_num FROM orderitems WHERE prod_id = 'TNT2';

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

| order_num |

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

|     20005 |

|     20007 |

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

2 rows in set (0.00 sec)

order_num ==> cust_id

(jlive)[crashcourse]>SELECT cust_id FROM orders WHERE order_num IN (20005,20007);

+---------+

| cust_id |

+---------+

|   10001 |

|   10004 |

+---------+

 

2 rows in set (0.00 sec)

cust_id ==> cust_name,cust_contact

(jlive)[crashcourse]>SELECT cust_name, cust_contact FROM customers WHERE cust_id IN (10001,10004);

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

| cust_name      | cust_contact |

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

| Coyote Inc.    | Y Lee        |

| Yosemite Place | Y Sam        |

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

 

2 rows in set (0.00 sec)

(jlive)[crashcourse]>SELECT cust_name, cust_contact FROM customers WHERE cust_id IN (SELECT cust_id FROM orders WHERE order_num  IN (SELECT order_num FROM orderitems WHERE prod_id = 'TNT2'));

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

| cust_name      | cust_contact |

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

| Coyote Inc.    | Y Lee        |

| Yosemite Place | Y Sam        |

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

 

2 rows in set (0.01 sec)

或

(jlive)[crashcourse]>SELECT cust_name, cust_contact FROM customers, orders, orderitems WHERE customers.cust_id = orders.cust_id AND orderitems.order_num = orders.order_num AND prod_id = 'TNT2';

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

| cust_name      | cust_contact |

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

| Coyote Inc.    | Y Lee        |

| Yosemite Place | Y Sam        |

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

 

2 rows in set (0.00 sec)

(jlive)[crashcourse]>SELECT cust_name, cust_contact FROM customers AS c, orders AS o, orderitems AS oi WHERE c.cust_id = o.cust_id AND oi.order_num = o.order_num AND prod_id = 'TNT2';

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

| cust_name      | cust_contact |

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

| Coyote Inc.    | Y Lee        |

| Yosemite Place | Y Sam        |

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

 

2 rows in set (0.00 sec)

子查询混合计算

(jlive)[crashcourse]>SELECT COUNT(*) AS orders FROM orders WHERE cust_id = 10001;

+--------+

| orders |

+--------+

|      2 |

+--------+

 

1 row in set (0.00 sec)

(jlive)[crashcourse]>SELECT cust_id, cust_name, cust_state, (SELECT COUNT(*) FROM orders WHERE orders.cust_id = customers.cust_id) AS orders FROM customers ORDER BY cust_name;

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

| cust_id | cust_name      | cust_state | orders |

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

|   10001 | Coyote Inc.    | MI         |      2 |

|   10005 | E Fudd         | IL         |      1 |

|   10002 | Mouse House    | OH         |      0 |

|   10003 | Wascals        | IN         |      1 |

|   10004 | Yosemite Place | AZ         |      1 |

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

 

5 rows in set (0.00 sec)