The character value is trimmed of leading and trailing pad characters and handled as if it was a string literal in the declaration of an INTERVAL string literal.
Character-to-INTERVAL conversion is supported for CHAR and VARCHAR types only. The source character type cannot be CLOB.
If the contents of the character string can be converted to a valid INTERVAL, then they are; otherwise, an error is returned.
You cannot convert a character data type of GRAPHIC to an INTERVAL string literal.