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'));
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';
SELECT cust_name,cust_contact FROM customers AS c,orders AS o,orderitems AS oi WHERE c.cust_id=o.cust_id AND o.order_num=oi.order_num AND oi.prod_id='TNT2';
SELECT prod_id,prod_name FROM products WHERE vend_id IN (SELECT vend_id FROM products WHERE prod_id='DTNTR');
SELECT p1.prod_id,p1.prod_name FROM products AS p1,products AS p2 WHERE p1.vend_id=p2.vend_id AND p2.prod_id='DTNTR';
SELECT customers.cust_id,orders.order_num FROM customers INNER JOIN orders ON customers.cust_id=orders.cust_id;
SELECT customers.cust_id,orders.order_num FROM customers LEFT OUTER JOIN orders ON customers.cust_id=orders.cust_id;
SELECT customers.cust_id,orders.order_num FROM customers RIGHT OUTER JOIN orders ON customers.cust_id = orders.cust_id;
SELECT customers.cust_id,customers.cust_name,COUNT(orders.order_num) FROM customers INNER JOIN orders ON customers.cust_id=orders.cust_id GROUP BY customers.cust_id;
SELECT customers.cust_id,customers.cust_name,COUNT(orders.order_num) FROM customers LEFT OUTER JOIN orders ON customers.cust_id=orders.cust_id GROUP BY customers.cust_id;
等值联结也叫内部联结。
等值联结：
SELECT vend_name,prod_name,prod_price FROM vendors,products WHERE vendors.vend_id=products.vend_id;
内部联结：
SELECT vend_name,prod_name,prod_price FROM vendors INNER JOIN products ON vendors.vend_id=products.vend_id;
联结多个表：
SELECT vend_name,prod_name,prod_price,quantity FROM vendors,products,orderitems WHERE vendors.vend_id=products.vend_id AND products.prod_id=orderitems.prod_id AND order_num=20005;
SELECT vend_name,prod_name,prod_price,quantity FROM vendors,products,orderitems WHERE vendors.vend_id=products.vend_id AND products.prod_id=orderitems.prod_id AND orderitems.order_num=20005;
（因为order_num只orderitems表有，所以不使用表名进行限定也是可以的）
使用子查询
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'));
使用等值联结
SELECT cust_name,cust_contact FROM customers,orders,orderitems WHERE customers.cust_id=orders.cust_id AND orders.order_num=orderitems.order_num AND orderitems.prod_id='TNT2';
列别名
SELECT Concat(RTrim(vend_name),' (',RTrim(vend_country),')') AS vend_title FROM vendors ORDER BY vend_name;
表别名
SELECT cust_name,cust_contact FROM customers AS c,orders AS o,orderitems AS oi WHERE c.cust_id=o.cust_id AND o.order_num=oi.order_num AND oi.prod_id='TNT2';
使用子查询
SELECT prod_id,prod_name FROM products WHERE vend_id IN (SELECT vend_id FROM products WHERE prod_id='DTNTR');
使用自联结
SELECT p1.prod_id,p1.prod_name FROM products AS p1,products AS p2 WHERE p1.vend_id=p2.vend_id AND p2.prod_id='DTNTR';
使用内部联结
SELECT customers.cust_id,orders.order_num FROM customers INNER JOIN orders ON customers.cust_id=orders.cust_id;
| cust_id | order_num |
| 10001 | 20005 |
| 10003 | 20006 |
| 10004 | 20007 |
| 10005 | 20008 |
使用外部联结：左联结，包含左表(customers)所有行
SELECT customers.cust_id,orders.order_num FROM customers LEFT OUTER JOIN orders ON customers.cust_id=orders.cust_id;
| cust_id | order_num |
| 10001 | 20005 |
| 10002 | NULL |
| 10003 | 20006 |
| 10004 | 20007 |
| 10005 | 20008 |
使用外部联结：右联结，包含右表(orders)所有行
SELECT customers.cust_id,orders.order_num FROM customers RIGHT OUTER JOIN orders ON customers.cust_id=orders.cust_id;
| cust_id | order_num |
| 10001 | 20005 |
| 10003 | 20006 |
| 10004 | 20007 |
| 10005 | 20008 |
使用聚集函数的内部联结
SELECT customers.cust_id,customers.cust_name,orders.order_num FROM customers INNER JOIN orders ON customers.cust_id=orders.cust_id;
| cust_id | cust_name | order_num |
| 10001 | Coyote Inc. | 20005 |
| 10003 | Wascals | 20006 |
| 10004 | Yosemite Place | 20007 |
| 10005 | The Fudds | 20008 |
SELECT customers.cust_id,customers.cust_name,COUNT(orders.order_num) AS num_orders FROM customers INNER JOIN orders ON customers.cust_id=orders.cust_id GROUP BY customers.cust_id;
| cust_id | cust_name | num_orders |
| 10001 | Coyote Inc. | 1 |
| 10003 | Wascals | 1 |
| 10004 | Yosemite Place | 1 |
| 10005 | The Fudds | 1 |
使用聚集函数的外部联结
SELECT customers.cust_id,customers.cust_name,orders.order_num FROM customers LEFT OUTER JOIN orders ON customers.cust_id=orders.cust_id;
| cust_id | cust_name | order_num |
| 10001 | Coyote Inc. | 20005 |
| 10002 | Mouse House | NULL |
| 10003 | Wascals | 20006 |
| 10004 | Yosemite Place | 20007 |
| 10005 | The Fudds | 20008 |
SELECT customers.cust_id,customers.cust_name,COUNT(orders.order_num) AS num_orders FROM customers LEFT OUTER JOIN orders ON customers.cust_id=orders.cust_id GROUP BY customers.cust_id;
| cust_id | cust_name | num_orders |
| 10001 | Coyote Inc. | 1 |
| 10002 | Mouse House | 0 |
| 10003 | Wascals | 1 |
| 10004 | Yosemite Place | 1 |
| 10005 | The Fudds | 1 |