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Converting Multiple Rows into a CSV String

Written by Chris Miller on 15 August 2000

Joern asks How do I aggregate data from multiple rows into a delimited list?

Joern writes "Dear SQL-Team: I want to condense several rows of a select.
mytable :
1 a
2 b
2 c
2 d
3 a

so that my select should result in

1 a
2 b,c,d
3 a

Of course it can be done with ASP (actually I do it this way), or in the db with fetching. But is there a simpler way to do it?"

I'm assuming by "fetching" you mean using cursors. We've run into this problem on several occasions, and the best we've come up with is to build a standard stored proc that takes as parameters a SQL Statement and opens a cursor and builds the string. Definitely not a very clean way to do it, but really the only way to do it in SQL Server at this point. Usually we use this for building a comma-delimited list for use in an "IN" clause for a query, specifically for search applications that allow multiple-select criteria. Here's what we use. The "@IsChar" is used to determine whether or not we need to put quotation marks around the returned strings (remember, we use this to build IN clauses). You may want to read up on using OUTPUT parameters in stored procs before using this stored proc. This won't do exactly what you specify, but it's a good starting point.

rocketscientist.

CREATE procedure sp_MakeCharList( @codelistselect varchar(1000), @delimitedlist varchar(8000) output, @IsChar bit = 0)
AS
begin
  set nocount on
  set rowcount 0

  declare @vcCurrentCol varchar(255)
  declare @vcCurrentList varchar(8000)
  declare @RC int

  create table #temptable (code varchar(255))
  insert into #temptable (code)
    exec(@codelistselect)

  set @RC = @@RowCount

  if @RC = 0
  begin
    set @DelimitedList = null
    return 0
  end

  declare SysCols insensitive scroll cursor
  for select code from #temptable
  for read only

  open SysCols

  fetch next from SysCols into @vcCurrentCol

  select @vcCurrentList = ''
  while @@Fetch_Status = 0
  begin
    if @IsChar = 1
      select @vcCurrentList = @vcCurrentList + quotename(@vcCurrentCol, '''') + ', '
    else
      select @vcCurrentList = @vcCurrentList + @vcCurrentCol + ', '

    fetch next from SysCols into @vcCurrentCol
  end

  close SysCols
  deallocate SysCols

  if @vcCurrentList = ''
    select @DelimitedList = null
  else
    --Remove the last ', '
    select @delimitedList = Substring(@vcCurrentList, 1, datalength(@vcCurrentList) - 2)

end

(Please also see this article on a set based approach to this problem.)