Sql server MS SQL：嵌套选择-神秘；无效的列名"；错误

当我对MSSQL 2000运行以下查询时

SELECT 
    DISTINCT(Email),
    (SELECT TOP 1 ActivityID
        FROM Activity aa, ActivityType tt 
        WHERE aa.ActivityTypeId = tt.ActivityTypeId 
            AND aa.ConsumerID = c.ConsumerID
            AND tt.ActivityType = 'Something_OptIn') optin,
    (SELECT TOP 1 ActivityID
        FROM Activity aa, ActivityType tt 
        WHERE aa.ActivityTypeId = tt.ActivityTypeId 
            AND aa.ConsumerID = c.ConsumerID
            AND tt.ActivityType = 'Something_OptOut') optout
FROM
    Activity a,
    Consumer c,
    ActivityType t
WHERE
    c.CountryID = '23'
    AND t.ActivityType = 'Something_Create'
    AND a.ActivityTypeId = t.ActivityTypeId
    AND c.ConsumerID = a.ConsumerID
    AND optin > 1

我得到以下错误

Server: Msg 207, Level 16, State 3, Line 1
Invalid column name 'optin'.

---

为什么会发生这种情况？我不明白为什么它会无效。

SQL Server不允许您在同一级别按名称引用别名。要解决此问题，请重复列定义：

WHERE
    c.CountryID = '23'
    AND t.ActivityType = 'Something_Create'
    AND a.ActivityTypeId = t.ActivityTypeId
    AND c.ConsumerID = a.ConsumerID
    AND (SELECT TOP 1 ActivityID
        FROM Activity aa, ActivityType tt 
        WHERE aa.ActivityTypeId = tt.ActivityTypeId 
            AND aa.ConsumerID = c.ConsumerID
            AND tt.ActivityType = 'Something_OptIn'
        ) > 1

或使用子查询：

SELECT  *
FROM    (
        SELECT 
            DISTINCT(Email),
            (...) optin,
            (...) optout
        FROM
            Activity a,
            Consumer c,
            ActivityType t
        ) as SubqueryAlias
WHERE
    c.CountryID = '23'
    AND t.ActivityType = 'Something_Create'
    AND a.ActivityTypeId = t.ActivityTypeId
    AND c.ConsumerID = a.ConsumerID
    AND optin > 1

---

最后一行

和optin>1

是罪犯

WHERE

子句对SELECT列表中的列别名一无所知

您可能应该子查询此SELECT而不使用有问题的条件，并将该条件应用于外部SELECT

SELECT *
FROM (
  SELECT
  ...
  WHERE ... /* everything except 'optin > 1' */
) anyAlias
WHERE optin > 1

---

它只适用于一个嵌套的SELECT，但不适用于optin和optout。请参阅。@jwandborg:您链接到的查询包含

=NULL

，但任何内容都不等于NULL。即使

null=null

也不是真的。您可能正在查找

为null

。