Subtype treatment

The static type of expression must be a user-defined structured type, and that type must be the same type as, or a supertype of, data-type. If the type name in data-type is unqualified, the SQL path is used to resolve the type reference. The static type of the result of subtype-treatment is data-type, and the value of the subtype-treatment is the value of the expression. At run time, if the dynamic type of the expression is not data-type or a subtype of data-type, an error is returned (SQLSTATE 0D000).

Example

• If an application knows that all column object instances in a column CIRCLE_COL have the dynamic type COLOREDCIRCLE, use the following query to invoke the method RGB on such objects. Assume the existence of a table called RINGS, with a column CIRCLE_COL of structured type CIRCLE. Also, assume that COLOREDCIRCLE is a subtype of CIRCLE and that the method RGB has been defined previously for COLOREDCIRCLE as RGB() RETURNS DOUBLE.

     SELECT TREAT (CIRCLE_COL AS COLOREDCIRCLE)..RGB()
       FROM RINGS

  At run time, if there are instances of dynamic type CIRCLE, an error is raised (SQLSTATE 0D000). This error can be avoided by using the TYPE predicate in a CASE expression, as follows:

     SELECT (CASE
       WHEN CIRCLE_COL IS OF (COLOREDCIRCLE)
         THEN TREAT (CIRCLE_COL AS COLOREDCIRCLE)..RGB()
         ELSE NULL
       END)
       FROM RINGS