Question

请检查此查询：

declare @T table
(
 FirstColumn datetime primary key,
 S_E1 float
)

insert into @T(FirstColumn, S_E1) values
('2012-01-01T00:00:01', 1),
('2012-01-01T00:00:02', 2),
('2012-01-01T00:00:03', 3),
('2012-01-01T00:00:04', 4),
('2012-01-01T00:00:05', 5),
('2012-01-01T00:00:06', 6)

declare @Take varchar = '1'
declare @StartDate varchar(10)='2012-01-01T00:00:01'
declare @EndDate varchar(10) = '2012-01-01T00:00:06'
declare @count varchar(Max)
DECLARE @SQL nvarchar(Max)
set @count = (select count(FirstColumn) from @T Where FirstColumn Between ''+@StartDate+'' and ''+@EndDate+'')

set @SQL =' select S_E1 from @T where S_E1 ='+ @Take+''

BEGIN try
while(CAST(@Take AS int) < CAST(@count AS int))
Begin

   print @SQL;  
   set @Take = CONVERT(varchar,CAST(@Take AS int)+1)

 end
END TRY
BEGIN CATCH
    select ERROR_MESSAGE() as errormessage
END CATCH

问题： 在上面的查询中，我无法更新@Take变量值。请让我知道我在哪里走错路。

Answer 1

更改了一些数据类型并将@SQL的赋值移到了循环中。

declare @T table
(
 FirstColumn datetime primary key,
 S_E1 float
)

insert into @T(FirstColumn, S_E1) values
('2012-01-01T00:00:01', 1),
('2012-01-01T00:00:02', 2),
('2012-01-01T00:00:03', 3),
('2012-01-01T00:00:04', 4),
('2012-01-01T00:00:05', 5),
('2012-01-01T00:00:06', 6)

declare @Take int = 1
declare @StartDate datetime = '2012-01-01T00:00:01'
declare @EndDate datetime = '2012-01-01T00:00:06'
declare @count int
declare @SQL nvarchar(Max)

set @count = (select count(FirstColumn)
              from @T
              where FirstColumn Between @StartDate and @EndDate)

begin try
  while @Take <= @count
  begin

     set @SQL =' select S_E1 from @T where S_E1 ='+ cast(@Take as varchar(10))+''
     print @SQL;  

     set @Take = @Take + 1
  end
end try
begin catch
    select error_message() as errormessage
end catch

使用while循环计数器更新动态where子句？

1 个答案: