SQL built-in functions complement inherent deficiencies in the nonprocedural language. They perform many tasks, ranging from rounding numbers to strings manipulation to conversion of data types into the sophisticated logic of substitute functions like DECODE.
While the number of functions defined in SQL92/99 standards is relatively small, every RDBMS vendor has its own set of these useful tools well in excess of hundreds. Therefore, it should not come as a surprise that functions differ across the vendors — in capability, implementation details, syntax, or simply being included or excluded from the implementation.
This chapter contains a comprehensive overview of the most important functions, as well as the correspondence between the three RDBMS implementations in terms of producing similar outcomes. The function classifications in this chapter are based on the data types of the arguments used by the functions to perform operations (for example, character data, numeric data, date), and on general functionalities (like conversion). Some functions that have advanced or nonstandard features are included in the chapters that discuss topics relevant to those functions: security functions are covered in the security chapter, and XML functions are part of the chapter on latest SQL developments.