[SilentSoul]

You should use cache_num_rows() as DobbysGamertag said.

pawn Код:

new query[126];
format(query, sizeof(query), "SELECT * FROM bantable WHERE BannedName = '%s' AND status = 1", GetPlayerNameEx(playerid));//Firstly we should select everything from your ban table however you named it.
mysql_tquery(mysql, query,"BanResults","i",playerid); //now we added a call back to check if this name is banned or not,


forward BanResults(playerid);
public BanResults(playerid)
{
    if(cache_num_rows(mysql) >=1)
    {
        //if this name was found.
    }
    else
    {
    //cannot find
    }
    return 1;
}

EDIT: This is a fast example taken from my gamemode, don't copy and paste you should modify it first!