如何在SQL Server 2012中的select查询中将值设置为变量？

Question

I want to generate a sequence for a complex query. For that purpose I have used a variable @rowNo .

My logic is :- If a field - isremoved = 0 then increase row number by 1.
If isremoved = 1 then increase row number by 1 only once till you find next 0.

This is so far I have done, but it gives me syntax error.

DECLARE @rowNo INT;
SET @rowNo = -1;

SELECT
case when sampleTable.isremoved = 0 then @rowNo + 1
    else @rowNo end
as rowNumber,
X,
Y,
Z
.
.
FROM tbl_sample sampleTable
INNER JOIN tbl_sample_2 sample2 ON sampleTable.id = sample2.id
.
.
.

This is my desire output :-

So what is the right way to achieve this kind of functionality in sql server 2012 ?

EDIT :- I do have one solution to use sub query to retrieve row number. But that will hit performance as it is very complex query (more than 20 joins) with huge amount of data. So please suggest me an alternative.

Answer 1

one way to do this is with subquery:

Select (Select count(*) from tbl_sample
        where id <= a.id 
            and a.isRemoved =1) rowNumber,
   X, Y, Z
From tbl_sample a
     Join tbl_sample_2 b 
         On b.id = a.id

Answer 2

In SQL Server 2012+, you can do what you want with a cumulative sum:

SELECT sum(case when sampleTable.isremoved = 0 then 1 else 0 end) over
            (order by . . .)
       . . .

The order by should repeat the order by in the outer query. You can also try using order by (select null)) . In my experience, this uses the ordering of the data in the outer query, but this is not documented to always work.

SQL Server does not allow you to set variables in a SELECT and to return values in a result set. One or the other, but not both.

Answer 3

I assume your rowNumber logic is equivalent to: if previous isremoved = 0 then increment rowNumber by 1, otherwise keep it as it is.

Using a combination of LAG and SUM ... OVER you can easily implement this logic:

SELECT id, isremoved,
       SUM(IIF(prevFlag = 0, 1, 0)) OVER (ORDER BY id) AS rowNumber
FROM (
SELECT a.id, isremoved,
       COALESCE(LAG(isremoved) OVER (ORDER BY a.id), isremoved) AS prevFlag
FROM tbl_sample AS a
INNER JOIN tbl_sample_2 AS b ON b.id = a.id) AS t

Demo here