School Commit Init

Anul 2/Semestrul 1/Baze de date/Lab 5/query.sql

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+-- Work on 3 tables of the form Ta(aid, a2, …), Tb(bid, b2, …), Tc(cid, aid, bid, …), where:
+
+-- aid, bid, cid, a2, b2 are integers;
+-- the primary keys are underlined;
+-- a2 is UNIQUE in Ta;
+-- aid and bid are foreign keys in Tc, referencing the primary keys in Ta and Tb, respectively.
+-- a. Write queries on Ta such that their execution plans contain the following operators:
+
+-- clustered index scan;
+-- clustered index seek;
+-- nonclustered index scan;
+-- nonclustered index seek;
+-- key lookup.
+-- b. Write a query on table Tb with a WHERE clause of the form WHERE b2 = value and analyze its execution plan. Create a nonclustered index that can speed up the query. Examine the execution plan again.
+
+-- c. Create a view that joins at least 2 tables. Check whether existing indexes are helpful; if not, reassess existing indexes / examine the cardinality of the tables.
+
+--a. Write queries on Ta such that their execution plans contain the following operators:
+
+-- clustered index scan;
+
+--create unique constraint on name column
+ 
+SELECT * FROM Players;
+
+-- clustered index seek;
+
+SELECT * FROM Players WHERE hmy = 22003;
+
+-- nonclustered index seek;
+
+-- add nonclustered index on name
+CREATE NONCLUSTERED INDEX IX_Players_name ON Players(hmy, name) INCLUDE (totalMatches);
+
+DROP INDEX IX_Players_name ON Players;
+
+SELECT name, totalMatches FROM Players WHERE name = 'lerio2';
+
+-- nonclustered index scan;
+
+SELECT name, totalMatches FROM Players WHERE totalMatches > 0;
+
+-- key lookup.
+
+-- write a query that uses the nonclustered index and a key lookup
+SELECT * FROM Players  WHERE name = 'lerio2';
+
+--b. Write a query on table Tb with a WHERE clause of the form WHERE b2 = value and analyze its execution plan. Create a nonclustered index that can speed up the query. Examine the execution plan again.
+
+-- create nonclustered index on b2
+CREATE NONCLUSTERED INDEX IX_Cards_faction_cardset ON Cards(hmy, faction, cardset) INCLUDE (name, cost);
+
+DROP INDEX IX_Cards_faction_cardset ON Cards;
+
+-- examine execution plan
+SELECT hmy, name, cost, faction, cardset FROM Cards WHERE faction = (SELECT hmy FROM Factions WHERE name='Neutral') AND cardset = (SELECT hmy FROM CardSet WHERE name='Base Set');
+
+--c. Create a view that joins at least 2 tables. Check whether existing indexes are helpful; if not, reassess existing indexes / examine the cardinality of the tables.
+
+-- create view
+GO
+
+ALTER VIEW CardsOwners AS
+SELECT Cards.name AS cardName, Players.name AS playerName, Cards.hmy AS cardId, Players.hmy AS playerId
+FROM Cards
+INNER JOIN CardsOwnership ON Cards.hmy = CardsOwnership.hCard
+INNER JOIN Players ON Players.hmy = CardsOwnership.hPlayer
+
+GO
+
+-- check if indexes are helpful
+
+SELECT * FROM CardsOwners;