无法使用 CONCAT、COALESCE 和 ISNULL 在 SQL 中连接 NULL 值

Question

我有一个包含多个连接的查询，我想将两列中的记录合并为一列。如果一列是空的，那么我想显示一列值作为结果。我尝试使用CONCAT、COALEASE 和ISNULL，但没有运气。我在这里错过了什么？

我的目标是，从查询中创建一个包含s.Script AS Original 和FromAnotherTable 组合的列。下面的查询运行但抛出Invalid column name 'Original' 和Invalid column name 'FromAnotherTable'。当我尝试使用CONCAT、COALEASE 或ISNULL 时。

SQL 查询：

SELECT DISTINCT
       c.Name AS CallCenter,
       LTRIM(RTRIM(s.Name)) Name,
       d.DNIS,
       s.ScriptId,
      s.Script AS Original,
      (
          SELECT TOP 5 CCSL.Line+'; ' 
          FROM CallCenterScriptLine CCSL
          WHERE CCSL.ScriptId = s.ScriptId
          ORDER BY ScriptLineId FOR XML PATH('')
       ) AS FromAnotherTable,
         --CONCAT(s.Script, SELECT TOP 5 CCSL.Line+'; ' FROM dbo.CallCenterScriptLine ccsl WHERE ccsl.ScriptId = s.ScriptId ORDER BY ccsl.ScriptLineId xml path(''))
         --CONCAT(Original, FromAnotherTable) AS Option1,
         --COALESCE(Original, '') + FromAnotherTable AS Option2,
         --ISNULL(Original, '') + FromAnotherTable AS Option3,,
       r.UnitName AS Store,
       r.UnitNumber
FROM CallCenterScript s WITH (NOLOCK)
     INNER JOIN CallCenterDNIS d WITH (NOLOCK) ON d.ScriptId = s.ScriptId
     INNER JOIN CallCenter c WITH (NOLOCK) ON c.Id = s.CallCenterId
     INNER JOIN CallCenterDNISRestaurant ccd WITH (NOLOCK) ON ccd.CallCenterDNISId = d.CallCenterDNISId
     INNER JOIN dbo.Restaurant r WITH (NOLOCK) ON r.RestaurantID = ccd.CallCenterRestaurantId
WHERE c.Id = 5
      AND (1 = 1)
      AND (s.IsDeleted = 0 OR s.IsDeleted IS NULL)
ORDER BY DNIS ASC;

输出：

这行得通：

DECLARE @Column1 VARCHAR(50) = 'Foo',
        @Column2 VARCHAR(50) = NULL;

SELECT CONCAT(@Column1,@Column2);
SELECT COALESCE(@Column2, '') + @Column1
SELECT ISNULL(@Column2, '') + @Column1

所以我不确定原始查询中缺少什么。

Answer 1

查看您获得的结果中的第 3 行。在您的连接列（Option1、2、3）中，您将获得第一个脚本列两次。不是你期望的第一个 + 第二个。

原因是因为您为子查询“脚本”起了别名，它与查询中的另一列同名，这使得它不明确。

更改子查询的别名，问题就会消失。坦率地说，我很惊讶您的查询没有引发错误。

编辑：您不能在同一查询级别的另一列定义中使用列别名。换句话说，你不能这样做：

SELECT 
  SomeColumn AS A
, (Subquery that returns a column) AS B
, A + B  --this is not allowed
FROM ...

您可以创建一个返回别名列的 CTE，然后在从 CTE 中选择的主查询中将它们连接起来，或者您必须使用别名的原始来源，如下所示：

SELECT 
  SomeColumn AS A
, (Subquery that returns a column) AS B
, SomeColumn  + (Subquery that returns a column)  --this is fine
FROM ...

Answer 2

我采用了另一种方法，在创建单独的列时，我在subQuery 中使用了ISNULL，它返回了我想要的结果。

查询：

SELECT DISTINCT
       c.Name AS CallCenter,
       LTRIM(RTRIM(s.Name)) Name,
       d.DNIS,
       s.ScriptId,
      s.Script AS Original,
      (
          SELECT TOP 5 ISNULL(CCSL.Line, '')+'; ' + ISNULL(s.Script, '')
          FROM CallCenterScriptLine CCSL
          WHERE CCSL.ScriptId = s.ScriptId
          ORDER BY ScriptLineId FOR XML PATH('')
       ) AS FromAnotherTable,
       r.UnitName AS Store,
       r.UnitNumber
FROM CallCenterScript s WITH (NOLOCK)
     INNER JOIN CallCenterDNIS d WITH (NOLOCK) ON d.ScriptId = s.ScriptId
     INNER JOIN CallCenter c WITH (NOLOCK) ON c.Id = s.CallCenterId
     INNER JOIN CallCenterDNISRestaurant ccd WITH (NOLOCK) ON ccd.CallCenterDNISId = d.CallCenterDNISId
     INNER JOIN dbo.Restaurant r WITH (NOLOCK) ON r.RestaurantID = ccd.CallCenterRestaurantId
WHERE c.Id = 5
      AND (1 = 1)
      AND (s.IsDeleted = 0 OR s.IsDeleted IS NULL)
ORDER BY DNIS ASC;

Answer 3

这是一个使用表变量的简化示例。

它使用 CROSS APPLY，而不是对字段使用子查询。

CONCAT 与 STUFF 结合用于将字符串粘合在一起。

declare @Foo table (fooID int identity(1,1) primary key, Script varchar(30));
declare @Bar table (barID int identity(1,1) primary key, fooID int, Line varchar(30));

insert into @Foo (Script) values 
('Test1'),('Test2'),(NULL);

insert into @Bar (fooID, Line) values 
(1,'X'),(1,'Y'),(2,NULL),(3,'X'),(3,'Y');

select  
 f.fooID, 
 f.Script,
 x.Lines,
 CONCAT(Script+'; ', STUFF(x.Lines,1,2,''))  as NewScript
from @Foo f
cross apply (
    select '; '+b.Line
    from @Bar b
    where b.fooID = f.fooID 
    FOR XML PATH('')
    ) x(Lines)

结果：

fooID Script  Lines   NewScript
----- ------- ------- -----------
1     Test1   ; X; Y  Test1; X; Y
2     Test2   NULL    Test2; 
3     NULL    ; X; Y  X; Y