FirebirdSQL logo
 SQL Language StructureCommon Language Elements 

Casting to a Domain

When you cast to a domain, any constraints declared for it are taken into account, i.e. NOT NULL or CHECK constraints.If the value does not pass the check, the cast will fail.

If TYPE OF is additionally specified — casting to its base type — any domain constraints are ignored during the cast.If TYPE OF is used with a character type (CHAR/VARCHAR), the character set and collation are retained.

Casting to TYPE OF COLUMN

When operands are cast to the type of a column, the specified column may be from a table or a view.

Only the type of the column itself is used.For character types, the cast includes the character set, but not the collation.The constraints and default values of the source column are not applied.

Example
CREATE TABLE TTT (
  S VARCHAR (40)
  CHARACTER SET UTF8 COLLATE UNICODE_CI_AI
);
COMMIT;

SELECT
  CAST ('I have many friends' AS TYPE OF COLUMN TTT.S)
FROM RDB$DATABASE;