How can I use join in case in SQL Server?

Question

How can I convert "in" to inner join in case:

SELECT 
    m.*, 
    atypcode_type = CASE 
                       WHEN m.[ATYPCODE] IS NOT NULL 
                            AND m.[ATYPCODE] IN (SELECT lastlevel 
                                                 FROM [dbo].[tbl2] 
                                                 WHERE ','+'2921'+',' LIKE '%,' + CAST([ParentId] AS VARCHAR(10)) + ',%') 
                          THEN 100
                       WHEN m.[ATYPCODE] IS NOT NULL 
                            AND m.[ATYPCODE] IN (SELECT lastlevel 
                                                 FROM [dbo].[tbl2]  
                                                 WHERE ',' + '3366' + ',' LIKE '%,' + CAST([ParentId] AS VARCHAR(10)) + ',%') 
                          THEN 101
                       ....
                    END
FROM 
    [tbl1] m
INNER JOIN
    [tbl2] ncg ON m.ATYPCODE = ncg.lastlevel 

How can I convert this code

m.[ATYPCODE] IN (SELECT lastlevel FROM [dbo].[tbl2] 
                 WHERE ','+'2921'+',' like '%,'+cast([ParentId] AS varchar(10))+',%')

to an inner join?

Result is :

atypcode    acurrcode   tarikh  atypcode_type
    2741    IRR 1397/06/31  109
    2941    IRR 1397/06/31  109
    3371    IRR 1397/06/31  101
    3381    IRR 1397/06/31  101
    3671    IRR 1397/06/31  101
    3381    IRR 1397/06/31  101
    4371    IRR 1397/06/31  101
    3971    IRR 1397/06/31  101
    3571    IRR 1397/06/31  101
    3771    IRR 1397/06/31  101

Create col atypcode_type with case, but this code it's too slow

Answer 1

This answers the question that you have asked:

SELECT m.*,
       (CASE WHEN m.[ATYPCODE] IS NOT NULL AND
                  t2_2921.lastlevel IS NOT NULL
             THEN 100
             WHEN m.[ATYPCODE] IS NOT NULL AND
                  t2_3366.lastlevel IS NOT NULL 
             THEN 101
             ....
        END) as atypcode_type
FROM [tbl1] m INNER JOIN
     [tbl2] ncg
     ON m.ATYPCODE = ncg.lastlevel LEFT JOIN
     tbl2 t2_2921
     ON m.ATYPCODE = t2_2921.lastlevel AND
        ',' + '2921' + ',' LIKE '%,' + CAST(?.ParentId AS VARCHAR(10)) + ',%') LEFT JOIN
     tbl2 t2_3366
     ON m.ATYPCODE = t2_3366.lastlevel AND
        ',' + '3366' + ',' LIKE '%,' + CAST(?.ParentId AS VARCHAR(10)) + ',%')

It does make the assumption that your delimited list has no duplicates.

The ? is for the table alias to identify where ParentId comes from.

I have a few editorial comments. First, I find it hard to imagine that this code does anything useful. It seems to be mixing levels and parents in a rather convoluted way. You haven't explained your data structure so this might be what you want.

Second, there is no performance gain from this. You don't specify why you want to switch to a JOIN . If that is the reason why, this has little benefit.

And that is related to the third reason. Do not store multiple values as comma-delimited lists. That is not the SQL way to store data. Relational databases have this great data structure to store lists. It is called a table , not a string .