Most expressions or functions in SQL expect a particular data type, for example, a CHAR or VARCHAR data type in a string function SUBSTR[ING]. If you wish to use a different data type, it must be converted first using the explicit conversion functions. For more information, see Conversion Functions.
Data types can be converted either explicitly or implicitly. If explicit conversion functions are not used, then the system attempts to perform an implicit conversion. If an implicit function is not possible or if one single value is not successfully converted during the computation, the system displays an error message.