Question

我是SQL Server的新手，有两个select语句 - 我正在尝试将UNION结合起来。但是我收到错误消息= 为变量赋值的SELECT语句不能与数据检索操作结合。

如何分配@NEWComments变量??

    DECLARE @NEWComments VARCHAR(max)         
    SELECT @NEWComments

    select cast(Comments1 as varchar(max)),cast( Comments2 as varchar(max)),   
    cast(Comments3 as varchar(max)), 
    from TableComments 
    where CommentsID = 1234
    UNION 

    SELECT TOP 2 @NEWComments = COALESCE(@NEWComments,'') + 
    cast(comments as varchar(max)) + ';'  
    FROM [ChildTableComments]
    where CommentsID = 1234

请帮助!!

我正在尝试从两个表TableComments和ChildTableComments中检索记录。 TableComments将具有atmax 1记录，但ChildTableComments将具有相同CommentsID的许多记录。

所以我试图从ChildTableComments获取Top2记录并添加它们并返回1个单独的列，可以使用UNION添加TableComments。

Answer 1

如果要将所有子注释合并为一行，可以这样做：

DECLARE @NEWComments VARCHAR(max);         
SET @NEWComments = '';

SELECT TOP 2 @NEWComments = @NEWComments + COALESCE(comments,'')
FROM [ChildTableComments]
where CommentsID = 1234;

select cast(Comments1 as varchar(max)) AS com1,
    cast( Comments2 as varchar(max)) as com2,
    cast(Comments3 as varchar(max)) as com3
from TableComments 
where CommentsID = 1234
UNION

SELECT @NEWComments AS com1,
    null as com2,
    null as com3;

Answer 2

您也可以尝试使用此

    DECLARE @NEWComments VARCHAR(max);         

    SELECT TOP 2 @NEWComments = @NEWComments + COALESCE(comments,'')
    FROM [ChildTableComments] where CommentsID = 1234;

    select @NEWComments AS Comments, cast(Comments1 as varchar(max)) AS com1,
    cast( Comments2 as varchar(max)) as com2,
    cast(Comments3 as varchar(max)) as com3
    from TableComments  where CommentsID = 1234

Answer 3

我不确定你要做什么。但UNION必须具有相同数量的列。我没有得到你想要做的任务。但这是一个可行的建议。我不确定Comments2陈述中Comments3和UNION应该是什么：

DECLARE @NEWComments VARCHAR(max)         
SELECT @NEWComments

select 
    cast(Comments1 as varchar(max)) Comments1,
    cast(Comments2 as varchar(max)) Comments2,   
    cast(Comments3 as varchar(max)) Comments3, 
from 
    TableComments 
where 
    CommentsID = 1234
UNION 

SELECT TOP 2 
    COALESCE(@NEWComments,'') + cast(comments as varchar(max)) + ';'  AS Comments1,
    '???' AS Comments2,
    '???' AS Comments3
FROM [ChildTableComments]
where CommentsID = 1234

尝试添加两个sql语句并使用SELECT语句获取错误

3 个答案: