# SQL Exercises/Pieces and providers

## ExercisesEdit

Select the name of all the pieces. (Seleccione el nombre de todas las piezas).

Click to see solution
``` SELECT Name FROM Pieces;
```

Select all the providers' data. (Seleccione todos los datos de los proveedores (providers)).

Click to see solution
``` SELECT * FROM Providers;
```

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

Click to see solution
```  SELECT Piece, AVG(Price)
FROM Provides
GROUP BY Piece;
```

Obtain the names of all providers who supply piece 1.

Click to see solution
``` /* 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);
```

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

Click to see solution
```/* 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
);
```

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).

Click to see solution
```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
);
```

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

Click to see solution
```INSERT INTO Provides
VALUES (1, 'TNBC', 7);
```

Increase all prices by one cent.

Click to see solution
```UPDATE Provides SET Price = Price + 1;
```

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

Click to see solution
```DELETE FROM Provides
WHERE Provider = 'RBT'
AND Piece = 4;
```

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

Click to see solution
```DELETE FROM Provides
WHERE Provider = 'RBT';
```

## Table creation codeEdit

```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 datasetEdit

```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);
```