The X/Open SQL CAE specification defined an escape clause as: "a syntactic mechanism for vendor-specific SQL extensions to be implemented in the framework of standardized SQL". Both DB2 CLI and ODBC support vendor escape clauses as defined by X/Open.
Currently, escape clauses are used extensively by ODBC to define SQL extensions. DB2 CLI translates the ODBC extensions into the correct DB2 syntax. The SQLNativeSql() function can be used to display the resulting syntax.
If an application is only going to access DB2 data sources, then there is no reason to use the escape clauses. If an application is going to access other data sources that offer the same support, but uses different syntax, then the escape clauses increase the portability of the application.
DB2 CLI used both the standard and shorthand syntax for escape clauses. The standard syntax has been deprecated (although DB2 CLI still supports it). An escape clause using the standard syntax took the form:
--(*vendor(vendor-identifier),
product(product-identifier) extended SQL text*)--
Applications should now only use the shorthand syntax, as described
below, to remain current with the latest ODBC standards.