Need expression for lookup function

Question

I need a lookup function:
Tablename: Tbl_orders
Fieldname to check OrdID = 1709 then make it 7001709 else keep numbers same.
Thank you very much for the helpful info.

Answer 1

For a lookup function, you'll always have a compare column (Column in the lookup table) and compare expression (Expression to which the compare column is compared to).
If you nest the lookup in decode / ifthenelse, the expression will be hard to maintain like:
decode(lookup(<DataStoreName>.Tbl_Orders, OrderID, 0, 'PRE_LOAD_CACHE',Compare_Column in Tbl_Orders, Compare expression with compare column) = 1709,lpad(lookup(<DataStoreName>.Tbl_Orders, OrderID, 0, 'PRE_LOAD_CACHE',Compare_Column in Tbl_Orders, Compare expression with compare column),7,'700'),lookup(<DataStoreName>.Tbl_Orders, OrderID, 0, 'PRE_LOAD_CACHE',Compare_Column in Tbl_Orders, Compare expression with compare column))
But, I believe you do not want to make the code this complex.
Do the lookup in one Query transform (either you can add as a function in the output schema or add it in mapping tab) and get the value in one Query transform.
lookup(<DataStoreName>.Tbl_Orders, OrderID, 0, 'PRE_LOAD_CACHE',Compare_Column in Tbl_Orders, Compare expression with compare column)
In the next Query transform, do an lpad / direct hardcoding inside ifthenelse / decode.
decode(Order_ID = 1709,lpad(Order_ID,7,'700'),Order_ID)