[Richie©]

You can do it this way;

pawn Code:

CheckAccountExists(account[])
{
    new string[128];
    format(string, sizeof(string), "SELECT * FROM player_accounts WHERE Name = '%s'", account);
    mysql_function_query(dbHandle, string, true, "CheckAccount", "s", account);
}

forward CheckAccount(account[]);
public CheckAccount(account[])
{
    new rows, fields;
    cache_get_data(rows, fields);
    
    if(!rows)
    {
        // account does not exist, register?
    }
    else
    {
        //proceed to login?
    }
    return 1; // To clear cache
}

If you want to do it the 'old' way, without CheckAccount callback, you can try y_inline which is supported in R31.