Question

Let’s say I have a table with five columns. Full select statement would be :

Select col1, col2, col3, col4, col5 
from tbl

But I need this query to be “dynamic”, every column must be possible to enable/disable. So, as far as I understand I need five tags (bool let’s say).
If i have tag1=0, tag2=1, tag3=1, tag4=0, tag5 =0 then the select statement should be like this:

Select col2, col3 
from tbl

If i have tag1=1, tag2=0, tag3=0, tag4=0, tag5 =0 then the select statement should be like this:

Select col1 
from tbl

So is there a possibility to do so in TSQL? I intend to create SP and execute it from php.

P.s. I understand that there’s a solution to make a bunch of IF statements with all possible tag1...tag5 variations, but this is not very effective when the number of columns (and enable tags) is high.

Answer 1

create procedure GetTblList
  @Tag1 bit,
  @Tag2 bit,
  @Tag3 bit,
  @Tag4 bit,
  @Tag5 bit
as

declare @SQL nvarchar(max)
set @SQL = 'select '

if @Tag1 = 1 set @SQL = @SQL + 'Col1,'
if @Tag2 = 1 set @SQL = @SQL + 'Col2,'
if @Tag3 = 1 set @SQL = @SQL + 'Col3,'
if @Tag4 = 1 set @SQL = @SQL + 'Col4,'
if @Tag5 = 1 set @SQL = @SQL + 'Col5,'
if @SQL = 'select ' set @SQL = @SQL + 'null as NoColumnSelected'

set @SQL = stuff(@SQL, len(@SQL), 1, ' from TbL')
exec (@SQL)