在等值连接中，该结果同时包括 manufact 和 stock 表中的 manu_code 列，原因是选择列表
请求每个列。
还可以使用附加约束创建等值连接，此时比较条件基于连接列中值的不相等性。这些连接
在 WHERE 子句中指定的比较条件中除等号（
=）之外还使用其他关系运算符。
要连接包含相同名称的列的表，用列的表名和句点（
.）限定每个列名，如下列查询所示。
图: 查询
SELECT order_num, order_date, ship_date, cust_calls.*
FROM orders, cust_calls
WHERE call_dtime >= ship_date
AND cust_calls.customer_num = orders.customer_num
ORDER BY orders.customer_num;
该查询连接 customer_num 列，然后只选择 cust_calls 表中 call_dtime 大于或等于 orders 表中
的 ship_date 那些行。该结果显示它返回的组合行。
order_num 1004
order_date 05/22/1998
ship_date 05/30/1998
customer_num 106 GBase 8s SQL 指南：教程
南大通用数据技术股份有限公司
61
call_dtime 1998-06-12 08:20
user_id maryj
call_code D
call_descr Order received okay, but two of the cans of
ANZ tennis balls within the case were empty
res_dtime 1998-06-12 08:25
res_descr Authorized credit for two cans to customer,
issued apology. Called ANZ buyer to report
the qa problem.
order_num 1008
order_date 06/07/1998
ship_date 07/06/1998
customer_num 110
call_dtime 1998-07-07 10:24
user_id richc
call_code L
call_descr Order placed one month ago (6/7) not received.
res_dtime 1998-07-07 10:30
res_descr Checked with shipping (Ed Smith). Order out
yesterday-was waiting for goods from ANZ.
Next time will call with delay if necessary.
order_num 1023
order_date 07/24/1998
ship_date 07/30/1998
customer_num 127
call_dtime 1998-07-31 14:30
user_id maryj
call_code I
call_descr Received Hero watches (item # 304) instead
of ANZ watches
res_dtime
res_descr Sent memo to shipping to send ANZ item 304
to customer and pickup HRO watches. Should
be done tomorrow, 8/1
