Add Support for Column List in Insert Clause

Include support for a list of columns in the insert clause of the merge statement. This helps when you may not know or care about the order of columns in the target table or if you don't want to have to insert values into all of the columns.

MERGE INTO target 
USING source ON b = y
WHEN MATCHED AND c + 1 + z > 0
THEN UPDATE SET a = 1, c = z
WHEN NOT MATCHED AND z IS NULL
THEN INSERT(a,b) VALUES(z, 7)