我正在尝试在SELECT语句中使用COUNT(*)。但是，我需要重新命名它，并能够为WHERE子句引用它。

我尝试过使用AS，我尝试省略AS，因为根据oracle页面似乎没有必要：https://docs.oracle.com/cd/B19306_01/server.102/b14200/functions032.htm

尝试将新标识符包装在引号中，但这也不起作用。

这是有效的，但是为计数提供了一个oracle生成的名称，这是不理想的，我不知道如何引用每行的计数：

SELECT

school_name,

(SELECT COUNT(*)

FROM liason_to

WHERE school_name = s.school_name)

FROM school s;

这是我尝试但不起作用的：

SELECT

school_name,

(SELECT COUNT(*) AS numLiasons

FROM liason_to

WHERE school_name = s.school_name)

FROM school s

WHERE numLiasons > 0;

它不会使列名称为“numLiasons”，并且末尾的where子句不知道numLiasons是什么，因此失败。

1

投票

您可以通过在其后面添加一个名称来为列添加别名，也可以在两者之间使用关键字AS。它与您对表格的处理基本相同。

SELECT school_name,

(SELECT count(*)

FROM liason_to l

WHERE l.school_name = s.school_name) AS numliasons

FROM school s;

或者干脆

SELECT school_name,

(SELECT count(*)

FROM liason_to l

WHERE l.school_name = s.school_name) numliasons

FROM school s;

但是你不能在WHERE子句中使用别名(在WHERE子句中的条件选择了记录之后发生了别名)。你必须重复这一尝试。

SELECT school_name,

(SELECT count(*)

FROM liason_to l

WHERE l.school_name = s.school_name) numliasons

FROM school s

WHERE (SELECT count(*)

FROM liason_to l

WHERE l.school_name = s.school_name) > 0;

1

投票

您可以使用连接和分组来避免子查询..并且您可以将您喜欢的anme指定为别名

SELECT s.school_name, COUNT(*) as my_count

FROM school s

INNER JOIN liason_to l on s.school_name = l.school_name

GROUP BY s.school_name

使用您的代码，您只需在(子选择)列上分配别名即可

SELECT

school_name,

(SELECT COUNT(*)

FROM liason_to

WHERE school_name = s.school_name) as my_name

FROM school s;

无论如何要过滤你可以使用的聚合结果但是对于count(*)记住这只适用于非空行，所以通常count(*)是> 0

0

投票

您不能在WHERE子句中引用别名，但您可以这样做：

SELECT

t.school_name,

t.numLiasons

FROM (

SELECT

s.school_name,

(

SELECT COUNT(*)

FROM liason_to

WHERE school_name = s.school_name

) AS numLiasons

FROM school s

) t

WHERE t.numLiasons > 0;