The SQL Selector operator supports a single SQL SELECT statement or multiple SELECT statements.
Certain restrictions apply when using a SQL SELECT statement in the SQL Selector operator:
- Do not specify a WITH clause with a SELECT statement. Use of a WITH or WITH BY clause produces an error message.
- Do not specify a USING modifier with a SELECT statement. Use of a USING modifier produces an error message.
The SQL Selector operator only logs on to one database session. Multiple SELECT statements are therefore sent as one request to the database. The database executes these multiple statements sequentially. Thus, the SQL Selector operator cannot take advantage of the parallel processing environment that Teradata PT offers. To take advantage of parallel processing, break multiple SQL SELECT statement requests into single SELECT statements carried by multiple SQL Selector operators, and then unite these data sources together with the UNION clause.