Question

Im building a dynamic sql update statement. This statement will update an unknown number of columns. Im looking for a clever way to set the commas between the columns in the update-statement correct.

DECLARE @UpdateSQL nvarchar(max) = 'UPDATE MYTABLE SET '
WHILE (somecondition)
BEGIN
    IF (someothercondition)
        SET @UpdateSQL = @UpdateSQL + @ColNameVar + ' = ' @ColNameVar + ',' --How to set this comma only on columns that are not the last??
END

There is ofcourse more building to do with this updateSQL, but this is the only relevant part for my question.

One important note is that the last run of the while-loop is not necessarly putting in a new column in the update, so i could not use that as a check.

Any ideas?

Using SQL Server-2008

Answer 1

After your loop, strip the last character?

SET @UpdateSQL = LEFT(@UpdateSQL, LEN(@UpdateSQL) - 1)

Change the position of the ‘,’ to the FRONT of the appended code, but don’t set it for the first one…

DECLARE @UpdateSQL nvarchar(max) = 'UPDATE MYTABLE SET ', @comma NVARCHAR(2) = ' '
WHILE (somecondition)
BEGIN
    IF (someothercondition)
    BEGIN
        SET @UpdateSQL = @UpdateSQL + @comma + @ColNameVar + ' = ' @ColNameVar
        SET @comma     = ', '
    END
END