How can I create a user-defined function in SQLite?

Question

I am developing an application in android and I need to create an udf in sqlite. Is it possible to create it in sqlite? And if yes how to do this?

Answer 1

SQLite does not have support for user-defined functions in the way that Oracle or MS SQL Server does. For SQLite, you must create a callback function in C/C++ and hook the function up using the sqlite3_create_function call.

Unfortunately, the SQLite API for Android does not allow for the sqlite3_create_function call directly through Java. In order to get it to work you will need to compile the SQLite C library with the NDK.

And if you are still interested read 2.3 User-defined functions...

Here's how to create a function that finds the first byte of a string.

static void firstchar(sqlite3_context *context, int argc, sqlite3_value **argv) {     if (argc == 1) {         char *text = sqlite3_value_text(argv[0]);         if (text && text[0]) {           char result[2];            result[0] = text[0]; result[1] = '\0';           sqlite3_result_text(context, result, -1, SQLITE_TRANSIENT);           return;         }     }     sqlite3_result_null(context); } 

Then attach the function to the database.

sqlite3_create_function(db, "firstchar", 1, SQLITE_UTF8, NULL, &firstchar, NULL, NULL) 

Finally, use the function in a sql statement.

SELECT firstchar(textfield) from table