Question

I have some option-item combination in my application from which the user can choose from, and hence to be queried from SQL Server to fetch some results

Let’s say the user choose combination like:

Option1 - Item1
Option1 - Item2
Option2 - Item1

Database table:

Option1     Item1     Details1    Details2    Details3
Option1     Item2     Details4    Details5    Details6
Option1     Item3     Details7    Details8    Details9
Option1     Item4     Details10   Details11   Details12
...
Option2     Item1     Details13   Details14   Details15

On selecting, the above option-item combination, their corresponding details are to be retrieved.

How do I fetch these details by passing in the Option-Item combination in the query?
I tried something like:

SELECT * FROM tbData 
  WHERE Strategy IN ('Option1','Option2') 
  AND Items IN ('Item1','Item2')

…but this gives the wrong answer.

Answer 1

You can’t use IN like that. You need to say:

WHERE (Strategy = 'Option1' AND Items IN ('Item1', 'Item2'))
OR (Strategy = 'Option2' AND Items IN ('Item1'))

This is because IN on each column separately means “return any rows where strategy is any value in (option 1 or option 2), and items is any value in (item 1 or item 2).” You can’t apply those two concepts separately and expect SQL Server to know that Item2 only applies to Option1.

---

Now, another option is to use a table-valued parameter. So you can define a table type as follows in SQL Server:

CREATE TYPE dbo.Options AS TABLE
(
    Strategy VARCHAR(32),
    Items    VARCHAR(32)
);

Populate a DataTable in C# with the selected options, then pass that in. Your query becomes:

CREATE PROCEDURE dbo.whatever
    @tvp dbo.Options READONLY
AS
BEGIN
    SELECT d.* FROM tbData AS d
      INNER JOIN @tvp AS t
      ON d.Strategy = t.Strategy
      AND d.Items = t.Items;
END
GO

---

EDIT adding yet another option.

If you can pass the set of options into your table as a dual-delimited string, e.g.

@Options = 'Option1,Item1;Option1,Item2;Option2,Item1'

Then you could use a table-valued function, e.g.

CREATE FUNCTION dbo.SplitMultiStrings
(
    @List VARCHAR(MAX),
    @d1   CHAR(1),
    @d2   CHAR(1)
)
RETURNS TABLE
AS
  RETURN 
  (
    SELECT x, y FROM 
    (
      SELECT
        x = i.i.value('(./x/text())[1]', 'varchar(32)'),
        y = i.i.value('(./y/text())[1]', 'varchar(32)')
      FROM (
        SELECT [XML] = CONVERT(XML, '<i><x>' 
          + REPLACE(REPLACE(@List, @d1, '</x><y>'),
          @d2, '</y></i><i><x>') + '</y></i>')
      ) AS x CROSS APPLY [XML].nodes('i') AS i(i)
    ) AS y WHERE x IS NOT NULL AND y IS NOT NULL
  );
GO

So now you can say:

CREATE PROCEDURE dbo.whatever
  @Options VARCHAR(MAX)
AS
BEGIN
  SET NOCOUNT ON;

  BEGIN TRY
    SELECT d.* 
      FROM dbo.SplitMultiStrings(@List, ',', ';') AS o
      INNER JOIN tbData AS d
      ON o.x = d.Strategy AND o.y = d.Items;
  END TRY
  BEGIN CATCH
    RAISERROR('You probably have a trailing ; or other formatting issue.', 11, 1);
  END CATCH
END
GO

And then call the stored procedure this way (by passing this comma/semi-colon-delimited string from your application):

EXEC dbo.whatever @Options = 'Option1,Item1;Option1,Item2;Option2,Item1';

But I still think the TVP option is the way to go.