打印选定的值

Question

如果有多个表，我想从这些表中找出col2为null时col1的值，并通过存储过程打印出来。

col1	col2
a	A
b	null
b	B
c	C
a	null

预期输出： a,b

--what I did but can not work

create proc sp_getValue
@tableName varchar(30)
as
declare @result nvarchar(max)
select distinct col1=@result　from @tableName
print @result

感谢您的帮助。

Answer 1

如果你想获取表名作为参数，你应该使用exec。

create proc sp_getValue
 @tableName varchar(30)
as
  exec('select distinct col1 from '+ quotename(@tableName) + ' where col2 is null'); 

要将此表转换为字符串，您可以将结果输出到某个临时表中，并使用游标遍历该表。像这样的：

DECLARE @value  NVARCHAR(30)
DECLARE @result NVARCHAR(100) = '';
CREATE TABLE #temp
(
    col1 NVARCHAR(30)
)

EXEC ('insert into #temp select col1 from ' + @tableName +' where col2 is null')

DECLARE myCur CURSOR FOR SELECT *
                         FROM #temp;
open myCur;
FETCH next from myCur  INTO @value;

WHILE @@FETCH_STATUS = 0
    BEGIN
        set @result = @result + @value + ',';
        FETCH next from myCur INTO @value;
    END

PRINT @result

close myCur;
DEALLOCATE myCur;