Question

我似乎在掌握使用AS创建别名的概念时会遇到一些麻烦，然后再使用该别名。下面是一个非常简单的查询示例，当我运行时出现错误：

SELECT IP,  
       (SELECT server_ip as IP  
          FROM table1  
         WHERE start_time BETWEEN @startdate AND @enddate  
      Group By server_ip)X  
Group By IP

我希望这只是从server_ip列中的第二个select语句返回结果。但是我收到一条错误消息，指出IP不是无效的列名。有人可以向我解释如何正确地做到这一点吗？

Answer 1

SELECT IP,
    (
    SELECT server_ip as IP
    FROM table1
    WHERE start_time BETWEEN @startdate AND @enddate
    Group By server_ip
    )X
/*FROM WHERE ? <--------------- */
Group By IP

目前您的SELECT声明

SELECT IP, X
GROUP BY IP

您需要一个FROM子句。 X目前是一个非相关的子查询。我怀疑你想把它当作一个派生表，但即使这样，查询也没有意义。无需执行两次相同的GROUP BY操作。

依赖于您的RDBMS，您也可以使用公用表表达式。这是一个有点人为的使用例子。

;WITH X AS
(
    SELECT server_ip as IP
    FROM table1
    WHERE start_time BETWEEN @startdate AND @enddate
),
Y AS
(
    SELECT IP
    FROM X
    Group By IP
)
SELECT IP
FROM Y

Answer 2

你错过了FROM子句：

  SELECT x.ip
    FROM (SELECT server_ip as IP  
            FROM table1  
           WHERE start_time BETWEEN @startdate AND @enddate  
        GROUP BY server_ip) AS x 
GROUP BY x.ip

原样，你只需要使用：

  SELECT server_ip as IP  
    FROM table1  
   WHERE start_time BETWEEN @startdate AND @enddate  
GROUP BY server_ip

Answer 3

您必须在新名称前使用AS关键字为临时表或列等分配别名。

sql使用别名

3 个答案: