SQL Exercises/Pieces and providers

Relational Schema

Exercises

1. Select the name of all the pieces.

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 SELECT Name FROM Pieces;

2. Select all the providers' data.

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 SELECT * FROM Providers;

3. Obtain the average price of each piece (show only the piece code and the average price).

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  SELECT Piece, AVG(Price)
    FROM Provides
GROUP BY Piece;

4. Obtain the names of all providers who supply piece 1.

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 /* Without subquery */
 SELECT Providers.Name
   FROM Providers INNER JOIN Provides
          ON Providers.Code = Provides.Provider
             AND Provides.Piece = 1;

/* With subquery */
 SELECT Name
   FROM Providers
  WHERE Code IN
   (SELECT Provider FROM Provides WHERE Piece = 1);

5. Select the name of pieces provided by provider with code "HAL".

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 /* Without subquery */
 SELECT Pieces.Name
   FROM Pieces INNER JOIN Provides
   ON Pieces.Code = Provides.Piece
     AND Provides.Provider = 'HAL';


 /* With IN subquery */
 SELECT Name
   FROM Pieces
   WHERE Code IN
     (SELECT Piece FROM Provides WHERE Provider = 'HAL');


 /* With EXISTS subquery */
 SELECT Name
   FROM Pieces
   WHERE EXISTS
   (
     SELECT * FROM Provides
       WHERE Provider = 'HAL'
         AND Piece = Pieces.Code
   );

6. For each piece, find the most expensive offering of that piece and include the piece name, provider name, and price (note that there could be two providers who supply the same piece at the most expensive price).

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 SELECT Pieces.Name, Providers.Name, Price
   FROM Pieces INNER JOIN Provides ON Pieces.Code = Piece
               INNER JOIN Providers ON Providers.Code = Provider
   WHERE Price =
   (
     SELECT MAX(Price) FROM Provides
     WHERE Piece = Pieces.Code
   );

7. Add an entry to the database to indicate that "Skellington Supplies" (code "TNBC") will provide sprockets (code "1") for 7 cents each.

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INSERT INTO Provides 
  VALUES (1, 'TNBC', 7);

8. Increase all prices by one cent.

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 UPDATE Provides SET Price = Price + 1;

9. Update the database to reflect that "Susan Calvin Corp." (code "RBT") will not supply bolts (code 4).

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 DELETE FROM Provides
   WHERE Provider = 'RBT'
     AND Piece = 4;

10. Update the database to reflect that "Susan Calvin Corp." (code "RBT") will not supply any pieces (the provider should still remain in the database).

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 DELETE FROM Provides
   WHERE Provider = 'RBT';

Table creation code

 CREATE TABLE Pieces (
   Code INTEGER PRIMARY KEY NOT NULL,
   Name TEXT NOT NULL
 );
 
 CREATE TABLE Providers (
  Code TEXT PRIMARY KEY NOT NULL,
  Name TEXT NOT NULL
 );
 
 CREATE TABLE Provides (
   Piece INTEGER  
     CONSTRAINT fk_Pieces_Code REFERENCES Pieces(Code),
   Provider TEXT
     CONSTRAINT fk_Providers_Code REFERENCES Providers(Code),
   Price INTEGER NOT NULL,
   PRIMARY KEY(Piece, Provider)
 );

Click to see MySQL syntax.

 CREATE TABLE Pieces (
  Code INTEGER PRIMARY KEY NOT NULL,
  Name TEXT NOT NULL
  );
 CREATE TABLE Providers (
  Code VARCHAR(40) 
  PRIMARY KEY NOT NULL,  
  Name TEXT NOT NULL 
  );
 CREATE TABLE Provides (
  Piece INTEGER, 
  FOREIGN KEY (Piece) REFERENCES Pieces(Code),
  Provider VARCHAR(40), 
  FOREIGN KEY (Provider) REFERENCES Providers(Code),  
  Price INTEGER NOT NULL,
  PRIMARY KEY(Piece, Provider) 
  );

Sample dataset

 INSERT INTO Providers(Code, Name) VALUES('HAL','Clarke Enterprises');
 INSERT INTO Providers(Code, Name) VALUES('RBT','Susan Calvin Corp.');
 INSERT INTO Providers(Code, Name) VALUES('TNBC','Skellington Supplies');
 
 INSERT INTO Pieces(Code, Name) VALUES(1,'Sprocket');
 INSERT INTO Pieces(Code, Name) VALUES(2,'Screw');
 INSERT INTO Pieces(Code, Name) VALUES(3,'Nut');
 INSERT INTO Pieces(Code, Name) VALUES(4,'Bolt');
 
 INSERT INTO Provides(Piece, Provider, Price) VALUES(1,'HAL',10);
 INSERT INTO Provides(Piece, Provider, Price) VALUES(1,'RBT',15);
 INSERT INTO Provides(Piece, Provider, Price) VALUES(2,'HAL',20);
 INSERT INTO Provides(Piece, Provider, Price) VALUES(2,'RBT',15);
 INSERT INTO Provides(Piece, Provider, Price) VALUES(2,'TNBC',14);
 INSERT INTO Provides(Piece, Provider, Price) VALUES(3,'RBT',50);
 INSERT INTO Provides(Piece, Provider, Price) VALUES(3,'TNBC',45);
 INSERT INTO Provides(Piece, Provider, Price) VALUES(4,'HAL',5);
 INSERT INTO Provides(Piece, Provider, Price) VALUES(4,'RBT',7);