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SQL 必知必会笔记11创建高级联结

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Release： 2016-06-07 17:39:16
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1. 使用表别名 SQL 除了可以对列名和计算字段使用别名，还允许给表名起别名。这样 做有两个主要理由： 缩短SQL 语句； 允许在一条SELECT 语句中多次使用相同的表。 使用表别名示例: 1 SELECT cust_name, cust_contact 2 FROM Customers AS C, Orders AS O, O

1. 使用表别名

SQL 除了可以对列名和计算字段使用别名，还允许给表名起别名。这样 做有两个主要理由：

  • 缩短SQL 语句；
  • 允许在一条SELECT 语句中多次使用相同的表。

    • 使用表别名示例:

    1 SELECT cust_name, cust_contact 2 FROM Customers AS C, Orders AS O, OrderItems AS OI 3 WHERE C.cust_id = O.cust_id 4 AND OI.order_num = O.order_num ; ，

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