The result of a CASE expression is displayed using the default format for the resulting data type. The result of a CASE expression does not apply the explicit format that may be defined for a column appearing in a THEN/ELSE expression.
Consider the following table definition:
CREATE TABLE duration (i INTEGER ,start_date DATE FORMAT 'EEEEBMMMBDD,BYYYY' ,end_date DATE FORMAT 'DDBM3BY4' );
Assume the default format for the DATE data type is 'YY/MM/DD'.
The following query displays the result of the CASE expression using the 'YY/MM/DD' default DATE format, not the format defined for the start_date or end_date columns:
SELECT i, CASE WHEN i=1 THEN start_date WHEN i=2 THEN end_date END FROM duration ORDER BY 1;