17.10 - Usage Notes - Advanced SQL Engine - Teradata Database

Teradata Vantageā„¢ - SQL Functions, Expressions, and Predicates

Advanced SQL Engine
Teradata Database
Release Number
Release Date
July 2021
Content Type
Programming Reference
Publication ID
English (United States)

WHEN clauses are processed sequentially.

The first WHEN clause search_condition_n that is TRUE returns the value of its associated scalar_expression_n as its result. The evaluation process then ends.

If no search_condition_n is TRUE, then scalar_expression_m, the argument of the ELSE clause, is the result.

If no ELSE clause is defined, then the default value for the result is NULL.

You can use a scalar subquery in the WHEN clause, THEN clause, and ELSE clause of a CASE expression. If you use a non-scalar subquery (a subquery that returns more than one row), a runtime error is returned.

Recommendation: Do not use the built-in functions CURRENT_DATE or CURRENT_TIMESTAMP in a CASE expression that is specified in a partitioning expression for a partitioned primary index (PPI). In this case, all rows are scanned during reconciliation.