syntax fixes on primary keys

constraint_9.sql

@@ -43,51 +43,51 @@ MODIFY (game_assists NOT NULL);
 -- alter primary keys
 
 ALTER TABLE players
-ADD CONSTRAINT pk_players
+ADD CONSTRAINT (pk_players)
 PRIMARY KEY player_id;
 
 ALTER TABLE teams
-ADD CONSTRAINT pk_teams
+ADD CONSTRAINT (pk_teams)
 PRIMARY KEY team_id;
 
 ALTER TABLE team_players
-ADD CONSTRAINT pk_team_players
+ADD CONSTRAINT (pk_team_players)
 PRIMARY KEY team_player_id;
 
 ALTER TABLE categories
-ADD CONSTRAINT pk_categories
+ADD CONSTRAINT (pk_categories)
 PRIMARY KEY genre_id;
 
 ALTER TABLE tournaments
-ADD CONSTRAINT pk_tournaments
+ADD CONSTRAINT (pk_tournaments)
 PRIMARY KEY tournament_id;
 
 ALTER TABLE tournament_participants
-ADD CONSTRAINT pk_tournament_participants
+ADD CONSTRAINT (pk_tournament_participants)
 PRIMARY KEY tournament_participant_id
 
 ALTER TABLE sponsors
-ADD CONSTRAINT pk_sponsors
+ADD CONSTRAINT (pk_sponsors)
 PRIMARY KEY sponsor_id;
 
 ALTER TABLE prizes
-ADD CONSTRAINT pk_prizes
+ADD CONSTRAINT (pk_prizes)
 PRIMARY KEY prize_id;
 
 ALTER TABLE rounds
-ADD CONSTRAINT pk_rounds
+ADD CONSTRAINT (pk_rounds)
 PRIMARY KEY round_id;
 
 ALTER TABLE games
-ADD CONSTRAINT pk_games
+ADD CONSTRAINT (pk_games)
 PRIMARY KEY game_id;
 
 ALTER TABLE statistics
-ADD CONSTRAINT pk_statistics
+ADD CONSTRAINT (pk_statistics)
 PRIMARY KEY game_result_id;
 
 ALTER TABLE game_participants
-ADD CONSTRAINT pk_game_participants
+ADD CONSTRAINT (pk_game_participants)
 PRIMARY KEY game_participant_id;
 
 -- alter unique