SQLite

** registered the application defined function.
*/
sqlite3 *sqlite3_context_db_handle(sqlite3_context*);

/*
** CAPI3REF: Function Auxiliary Data
**
** The following two functions may be used by scalar SQL functions to
** associate metadata with argument values. If the same value is passed to
** multiple invocations of the same SQL function during query execution, under
** some circumstances the associated metadata may be preserved. This might
** be used, for example, in a regular-expression matching
** function. The compiled version of the regular expression is stored as
** metadata associated with the SQL value passed as the regular expression

** pattern.  The compiled regular expression can be reused on multiple
** invocations of the same function so that the original pattern string
** does not need to be recompiled on each invocation.
**
** ^The sqlite3_get_auxdata() interface returns a pointer to the metadata
** associated by the sqlite3_set_auxdata() function with the Nth argument
** value to the application-defined function. ^If no metadata has been ever
** been set for the Nth argument of the function, or if the corresponding
** function parameter has changed since the meta-data was set,
** then sqlite3_get_auxdata() returns a NULL pointer.
**
** ^The sqlite3_set_auxdata(C,N,P,X) interface saves P as metadata for the N-th
** argument of the application-defined function.  ^Subsequent
** calls to sqlite3_get_auxdata(C,N) return P from the most recent
** sqlite3_set_auxdata(C,N,P,X) call if the data has not been dropped, or
** NULL if the data has been dropped.

** ^(If it is not NULL, SQLite will invoke the destructor
** function X passed to sqlite3_set_auxdata(C,N,P,X) when <ul>

** <li> the corresponding function parameter changes,
** <li> [sqlite3_reset()] or [sqlite3_finalize()] is called for the
**      SQL statement,
** <li> sqlite3_set_auxdata() is invoked again on the same parameter, or

** <li> a memory allocation error occurs. </ul>)^
**
** SQLite is free to call the destructor and drop metadata on any
** parameter of any function at any time.  ^The only guarantee is that
** the destructor will be called when the [prepared statement] is destroyed.
** Note in particular that the destructor X in the call to
** sqlite3_set_auxdata(C,N,P,X) might be called immediately, before
** the sqlite3_set_auxdata() call even returns.  Hence sqlite3_set_auxdata()
** should be called near the end of the function implementation and the
** implementation should not make any use of P after sqlite3_set_auxdata()
** has been called.
**
** ^(In practice, metadata is preserved between function calls for
** function parameters that are compile-time constants, including literal
** values and [parameters] and expressions composed from the same.)^
**
** These routines must be called from the same thread in which
** the SQL function is running.