sqlite3_create_function(), sqlite3_create_function16(), sqlite3_create_function_v2(), sqlite3_create_window_function()

 ... The sixth, seventh and eighth parameters passed to the three "sqlite3_create_function*" functions, xFunc, xStep and xFinal, are pointers to C-language functions that implement the SQL function or aggregate. A scalar SQL function requires an implementation of the xFunc callback ... 

 ... Normal functions specify only xFunc and leave xStep and xFinal set to NULL. Aggregate functions specify xStep and xFinal and leave xFunc set to NULL. There is no separate sqlite3_create_aggregate() API. The function name is specified in UTF-8. A ... 

sqlite3_result_blob(), sqlite3_result_blob64(), sqlite3_result_double(), sqlite3_result_error(), sqlite3_result_error16(), sqlite3_result_error_toobig ... 

These routines are used by the xFunc or xFinal callbacks that implement SQL functions and aggregates. See sqlite3_create_function() and sqlite3_create_function16() for additional information. These functions work very much like the parameter binding family of functions used to bind values to ... 

 ... For regular functions, the xFunc callback is invoked once for each function call. The implementation of xFunc should call one of the sqlite_set_result_... interfaces to return its result. The sqlite_user_data() routine can be used to retrieve the pUserData pointer that ... 

2.3.1. The Scalar Function Callback Scalar SQL functions are implemented by a single callback in the xFunc parameter to sqlite3_create_function(). The following code demonstrations the implementation of a "noop(X)" scalar SQL function that merely returns its argument: static void noopfunc( sqlite3_context *context, int argc ...