When you use pushdown optimization, the Integration Service converts the expression in the transformation or workflow link by determining equivalent operators, variables, and functions in the database. If there is no equivalent operator, variable, or function, the Integration Service processes the transformation logic. For example, the Integration Service translates the aggregate function STDDEV() to STDDEV_SAMP() on Teradata and to STDEV() on Microsoft SQL Server. The Integration Service processes any transformation that uses the FIRST() aggregate function because no database supports this function.
The Integration Service logs a message in the workflow log and the Pushdown Optimization Viewer when it cannot push an expression to the database. Use the message to determine the reason why it could not push the expression to the database.
The tables in this section summarize the availability of PowerCenter operators, variables, and functions in databases.