join comma delimited data column

Question

my table1 is :

T1

col1    col2
 C1     john
 C2     alex
 C3     piers
 C4     sara

and so table 2:

T2

Answer 1

Here's a way of splitting the data without a function, then using the standard XML PATH method for getting the CSV list:

with CTE as
(
  select T2.col1
    , T1.col2
  from T2
    inner join T1 on charindex(',' + T1.col1 + ',', ',' + T2.col2 + ',') > 0
)
select T2.col1
  , col2 = stuff(
      (
        select ',' + CTE.col2
        from CTE
        where T2.col1 = CTE.col1
        for xml path('')
      )
      , 1
      , 1
      , ''
    )
from T2

SQL Fiddle with demo.

As has been mentioned elsewhere in this question it is hard to query this sort of denormalised data in any sort of efficient manner, so your first priority should be to investigate updating the table structure, but this will at least allow to get the results you require.