Question

This is my first time trying to create an udf for mysql. The docs state that my_func_init gets called prior to executing the main function, yet in my environment this does not seem to happen.

long long charmatch(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error)
{
    return 42;
}

my_bool charmatch_init(UDF_INIT *initid, UDF_ARGS *args, char *message)
{
    if (args->arg_count != 2)
    {
        strncpy(message, "charmatch() requires two arguments", 34);
        return EXIT_FAILURE;
        // was return EXIT_SUCCESS;
    }

    if(args->arg_type[0] != STRING_RESULT)
    {
        strncpy(message, "argument 1 must be a string", 27);
        return EXIT_FAILURE;
        // was return EXIT_SUCCESS;
    }

    if(args->arg_type[0] != STRING_RESULT)
    {
        strncpy(message, "argument 2 must be a string", 27);
        return EXIT_FAILURE;
        // was return EXIT_SUCCESS;
    }

    return EXIT_SUCCESS;
}

As you can see, I’m checking whether there are two arguments. In theory SELECT CHARMATCH() should return a message saying I must set two arguments, but it’s not: it return 42.

Why doesn’t it return the message?

EDIT Seems like the problem was in my return values for errors being 0 instead of 1. I fixed it and now calling SELECT CHARMATCH() with the wrong number of arguments returns an empty set. Why are the errors not being displayed?

Answer 1

You always return EXIT_SUCCESS in charmatch_init(), but

“The initialization function should return 0 if no error occurred and 1 otherwise. If an error occurs, xxx_init() should store a null-terminated error message in the message parameter. ”

http://dev.mysql.com/doc/refman/5.0/en/udf-return-values.html

I guess that’s why your error messages are ignored.