MariaDB で、UDF (User-Defined Function) を使う

// ----------------------------------------------------------------------
//
//  msec.c
//
//                      May/19/2017
// ----------------------------------------------------------------------
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <sys/time.h>
#include <mysql.h>

// ----------------------------------------------------------------------
my_bool msec_init(UDF_INIT *initid, UDF_ARGS *args, char *message)
{
    return 0;
}

// ----------------------------------------------------------------------
void msec_deinit(UDF_INIT *initid __attribute__((unused)))
{
}

// ----------------------------------------------------------------------
char *msec(UDF_INIT *initid __attribute__((unused)),
    UDF_ARGS *args, char *result, unsigned long *length,
    char *is_null, char *error __attribute__((unused)))
{
    struct timeval tv;
    struct tm *tmptr = NULL;

    is_null = 0;

    gettimeofday(&tv, NULL);
    tmptr = localtime(&tv.tv_sec);

    if(args->arg_count > 0 && ! strcmp( args->args[0], "epoch")){
        sprintf(result, "Msec: %ld.%03ld",
            tv.tv_sec,
            tv.tv_usec / 1000);
    }
    else{
        sprintf(result, "Msec: %04d/%02d/%02d %02d:%02d:%02d:%03ld",
            tmptr->tm_year + 1900, tmptr->tm_mon + 1,
            tmptr->tm_mday, tmptr->tm_hour,
            tmptr->tm_min, tmptr->tm_sec,
            tv.tv_usec / 1000);
    }

    *length = strlen(result);

    return result;
}

// ----------------------------------------------------------------------

gcc -Wall -I/usr/include/mysql -shared -o msec.so -fPIC msec.c

sudo systemctl restart mysqld

$ mysql -uroot
MariaDB [(none)]> create function msec returns string soname 'msec.so';
MariaDB [(none)]> select msec ();
+-------------------------------+
| msec ()                       |
+-------------------------------+
| Msec: 2017/05/19 07:42:50:744 |
+-------------------------------+
1 row in set (0.00 sec)