pawn Код:
new playername[MAX_PLAYER_NAME], query[128];
GetPlayerName(playerid, playername, sizeof(playername));
mysql_real_escape(playername, playername); // cleaning player's name
format(query, sizeof(query), "SELECT * FROM `usuarios` WHERE UserName = '%s'", playername); // format query
mysql_query(query); // query
mysql_store_result(); // store results
if(mysql_num_rows() == 1) PlayerInfo[playerid][Registered] = 1; // check results
else PlayerInfo[playerid][Registered] = 0;
mysql_free_result(); // clean memory
That's how you should do it.