Transformations > Lookup transformation > Lookup SQL overrides
  

Lookup SQL overrides

When a mapping includes a Lookup transformation, the mapping task queries the lookup object based on the fields and properties that you configure in the Lookup transformation. The mapping task runs a default lookup query when the first row of data enters the Lookup transformation. If the Lookup transformation performs a relational lookup, you can override the default query.
The default query contains a SELECT statement that includes all lookup fields in the mapping. The SELECT statement also contains an ORDER BY clause that orders all columns in the same order in which they appear in the Lookup transformation. To view the default query, run the mapping task. The default query appears in the log file.
If you want to change the ORDER BY clause, add a WHERE clause, or transform the lookup data before it is cached, you can override the default query. For example, you might use database functions to adjust the data types or formats in the lookup table to match the data types and formats of fields that are used in the mapping. Or, you might override the default query to query multiple tables.
Override the default query on the Advanced tab of the Lookup transformation. Enter the entire SELECT statement in the Lookup SQL Override field. Use an alias for each column in the query. If you want to change the ORDER BY clause, you must also append "--" to the end of the query to suppress the ORDER BY clause that the mapping task generates.

Example

A Lookup transformation returns the following fields from Microsoft SQL Server table ALC_ORDER_DETAILS:
The Return Fields tab of the Lookup transformation lists the following return fields from table ALC_ORDER_DETAILS: ORDERID, PRODUCTID, UNITPRICE, QUANTITY, and DISCOUNT.
The transformation uses the following lookup condition:
ORDERID=in_ORDERID
When you run the mapping task, the following query appears in the log file:
LKPDP_1> DBG_21097 [2018-11-07 14:11:33.509] Lookup Transformation [lkp_ALC_ORDER_DETAILS]: Default sql to create lookup cache: SELECT PRODUCTID,UNITPRICE,QUANTITY,DISCOUNT,ORDERID FROM "icsauto"."ALC_ORDER_DETAILS" ORDER BY ORDERID,PRODUCTID,UNITPRICE,QUANTITY,DISCOUNT
To override the ORDER BY clause and sort by PRODUCTID, enter the following query in the Lookup SQL Override field on the Advanced tab:
SELECT PRODUCTID AS PRODUCTID, UNITPRICE AS UNITPRICE, QUANTITY AS QUANTITY, DISCOUNT AS DISCOUNT, ORDERID AS ORDERID FROM "icsauto"."ALC_ORDER_DETAILS" ORDER BY PRODUCTID --
When you run the mapping task again, the following query appears in the log file:
LKPDP_1> DBG_21312 [2018-11-07 14:14:36.734] Lookup Transformation [lkp_ALC_ORDER_DETAILS]: Lookup override sql to create cache: SELECT PRODUCTID AS PRODUCTID, UNITPRICE AS UNITPRICE, QUANTITY AS QUANTITY, DISCOUNT AS DISCOUNT, ORDERID AS ORDERID FROM "icsauto"."ALC_ORDER_DETAILS" ORDER BY PRODUCTID -- ORDER BY ORDERID,PRODUCTID,UNITPRICE,QUANTITY,DISCOUNT

Guidelines for overriding the lookup query

Certain rules and guidelines apply when you override a lookup query.
Use the following guidelines: