When you create an external procedure, the database stores the current session time zone for the procedure along with its definition to enable the SQL language elements in the procedure to execute in a consistent time zone and produce consistent results. However, time or timestamp data passed as an input parameter to the procedure still use the runtime session time zone rather than the creation time zone for the procedure.
The AT TIME ZONE option of the ALTER PROCEDURE statement enables you to reset the time zone for all of the SQL elements of external procedures when you recompile a procedure. The database then stores the newly specified time zone as the creation time zone for the procedure.
You can only specify AT TIME ZONE with the COMPILE option, and it must follow the COMPILE specification. If it does not, the database aborts the request and returns an error to the requestor. For details, see the information about ALTER PROCEDURE (External Form) in Teradata Vantage™ - SQL Data Definition Language Detailed Topics, B035-1184.