public OnPlayerConnect(playerid)
{
    //RESERTTING VARIABLES:
    IsNewHere[playerid] = false;
    MaxLoginAmount[playerid] = 0;
    for(new playerdata:e; e < playerdata; ++e)
    pData[playerid][e] = 0;
    
    new query[128]; //We use this variable to format our query
    GetPlayerName(playerid, Name[playerid], 24); //Getting player's name
    GetPlayerIp(playerid, IP[playerid], 16); //Getting layer's IP
    mysql_format(mysql, query, sizeof(query),"SELECT `Password`, `ID` FROM `players` WHERE `Username` = '%e' LIMIT 1", Name[playerid]);
    // - We use mysql_format instead of format because we can use an %e specifier. %e specifier escapes a string so we can avoid sql injection which means we don't have to use mysql_real_escape_string
    // - Formatting our query; SELECT `Password`, `ID` FROM `players` WHERE `Username`='%e' means we are selecting a Password and ID's column in the table that has player's name in Username column.
    // - LIMIT 1; we only need 1 result to be shown
    mysql_tquery(mysql, query, "OnAccountCheck", "i", playerid);
    //lets execute the formatted query and when the execution is done, a callback OnAccountCheck will be called
    //You can name the callback however you like
    return 1;
}

public OnAccountCheck(playerid)
{
    new str[200];
    new rows, fields;
    cache_get_data(rows, fields, mysql);
    if(rows)
    {
        cache_get_field_content(0, "PASS", pData[playerid][Password], mysql, 129);
        pData[playerid][ID] = cache_get_field_content_int(0, "ID");
        printf("%s", pData[playerid][Password]); //Debug
        format(str, sizeof(str), "Welcome back to Reindience Roleplay, %s! \nLooks like your account is registered, please enter your password below:", GPName(playerid));
        ShowPlayerDialog(playerid, DIALOG_LOG, DIALOG_STYLE_PASSWORD, "Welcome back to Reindience Roleplay!", str, "Login", "Quit");
    }
    else
    {
        format(str, sizeof(str), "Welcome to Reindience Roleplay, %s! \nLooks like your account is not registered, please enter a password below:", GPName(playerid));
        ShowPlayerDialog(playerid, DIALOG_REG, DIALOG_STYLE_PASSWORD, "Welcome to Reindience Roleplay!", str, "Register", "Quit");
    }
    return 1;
}