Joe Celko's SQL for Smarties, 3rd Edition

5.3. Common Vendor Extensions

The original SQL-89 standard did not define any functions for CHAR(n) data types. Standard SQL added the basic functions that have been common to implementations for years. However, there are other common or useful functions, and it is worth knowing how to implement them outside of SQL.

Many vendors also have functions that will format data for display by converting the internal format to a text string. A vendor whose SQL is tied to a 4GL is much more likely to have these extensions, simply because the 4GL can use them. The most common one converts a date and time to a national format.

These functions generally use either a COBOL-style PICTURE parameter or a globally set default format. Some of this conversion work ...