15.10 - Example: Collecting Statistics on Built-In Function Expressions - Teradata Database

Teradata Database SQL Data Definition Language Syntax and Examples

prodname
Teradata Database
vrm_release
15.10
created_date
December 2015
category
Programming Reference
featnum
B035-1144-151K

You can also collect statistics on constant expressions that refer to built-in functions.

The Optimizer remembers the materialized values for the CURRENT_TIMESTAMP, CURRENT_DATE and USER functions when statistics are collected and then substitutes the stored materialized values when the statistics are used.

For other built-in functions like SESSION and CURRENT_ROLE, the Optimizer substitutes the values based on the session parameters at the time the statistics are used. Even though Teradata Database allows you to specify any built-in functions, you should restrict your collecting of statistics to built-in functions other than CURRENT_TIMESTAMP, CURRENT_DATE and USER in the expressions.

In the following request, the Optimizer substitutes the value for CURRENT_DATE for the CASE expression and then remembers it. When the statistics are used for this expression, the Optimizer substitutes the saved value for CURRENT_DATE.

     COLLECT STATISTICS 
     COLUMN CASE WHEN CAST(o_orderdatetime AS DATE AT 0) = CURRENT_DATE 
                 THEN 'orders-today'
                 ELSE 'orders-old'
            END AS stats_orders_today_and_old
     ON orders;