Sql – Prefix all columns in T-SQL statement

sql servertsql

Given a table "ABC" with columns Col1, Col2 and Col3 it is possible to automatically generate something like the following:

SELECT
Col1 AS 'ABC_Col1', 
Col2 AS 'ABC_Col2',
Col3 AS 'ABC_Col3' 
FROM ABC

I have a table without a fixed set of columns (users are able to append their own columns) where I still need the column prefix (because it is needed in a JOIN/CTE with other tables that also have columns with the names Col1, Col2 etc…)

Therefore I would like to be able to write something like this:

SELECT
T0.* AS 'ABC_T.*', 
FROM ABC T0

Which is of course not valid SQL, but can it be done somehow so the "*" columns all get the same prefix?

Best Answer

This will give you a map of old column names and new column names:

SELECT syscolumns.name as old_column_name, 'ABC_' + syscolumns.name as new_column_name
   FROM sysobjects 
        JOIN syscolumns ON sysobjects.id = syscolumns.id
   WHERE sysobjects.name = 'ABC'
ORDER BY sysobjects.name,syscolumns.colid

From there it's just some dynamic sql. I'm still playing with it.

EDIT

OK, I ditched that.

DECLARE @sql varchar(max)
SET @sql = 'SELECT '

DECLARE @old_column_name varchar(50)
DECLARE @getNext CURSOR
SET @getNext = CURSOR FOR 
    SELECT syscolumns.name
       FROM sysobjects 
            JOIN syscolumns ON sysobjects.id = syscolumns.id
       WHERE sysobjects.name = 'ABC'
OPEN @getNext
FETCH NEXT FROM @getNext INTO @old_column_name
WHILE @@fetch_status = 0
BEGIN

    --BUILD DYNAMIC SQL
    SET @sql = @sql + @old_column_name + ' AS ''ABC_' + @old_column_name + ''', '

FETCH NEXT FROM @getNext INTO @old_column_name
END
CLOSE @getNext
DEALLOCATE @getNext

--REMOVE FINAL COMMA AND ADD TABLE
SET @sql = SUBSTRING(@sql, 0, LEN(@sql)) + ' FROM ABC'

exec(@sql)

A) this is terrible performance (because it's a cursor)

B) I know you're not meant to do work for people on here, but I got carried away.

C) I considered not even posting this because of how poor of an answer I feel it is, but it's a least an idea.

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