# SQL Exercises/The warehouse

## Exercises

1. Select all warehouses.

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

2. Select all boxes with a value larger than \$150.

Click to see solution
``` SELECT * FROM Boxes
WHERE Value > 150;
```

3. Select all distinct contents in all the boxes.

Click to see solution
``` SELECT DISTINCT Contents
FROM Boxes;
```

4. Select the average value of all the boxes.

Click to see solution
``` SELECT AVG(Value)
FROM Boxes;
```

5. Select the warehouse code and the average value of the boxes in each warehouse.

Click to see solution
```  SELECT Warehouse, AVG(Value)
FROM Boxes
GROUP BY Warehouse;
```

6. Same as previous exercise, but select only those warehouses where the average value of the boxes is greater than 150.

Click to see solution
```  SELECT Warehouse, AVG(Value)
FROM Boxes
GROUP BY Warehouse
HAVING AVG(Value) > 150;
```

7. Select the code of each box, along with the name of the city the box is located in.

Click to see solution
```  SELECT Boxes.Code, Location
FROM Warehouses INNER JOIN Boxes
ON Warehouses.Code = Boxes.Warehouse;
```

8. Select the warehouse codes, along with the number of boxes in each warehouse. Optionally, take into account that some warehouses are empty (i.e., the box count should show up as zero, instead of omitting the warehouse from the result).

Click to see solution
``` /* Not taking into account empty warehouses */
SELECT Warehouse, COUNT(*)
FROM Boxes
GROUP BY Warehouse;

/* Taking into account empty warehouses */
SELECT Warehouses.Code, COUNT(Boxes.Code)
FROM Warehouses LEFT JOIN Boxes
ON Warehouses.Code = Boxes.Warehouse
GROUP BY Warehouses.Code;
```

9. Select the codes of all warehouses that are saturated (a warehouse is saturated if the number of boxes in it is larger than the warehouse's capacity).

Click to see solution
``` SELECT Code
FROM Warehouses
WHERE Capacity <
(
SELECT COUNT(*)
FROM Boxes
WHERE Warehouse = Warehouses.Code
);

/* Alternate method not involving nested statements */
SELECT Warehouses.Code
FROM Warehouses JOIN Boxes ON Warehouses.Code = Boxes.Warehouse
GROUP BY Warehouses.code, Warehouses.Capacity
HAVING Count(Boxes.code) > Warehouses.Capacity
```

10. Select the codes of all the boxes located in Chicago.

Click to see solution
``` /* Without subqueries */
SELECT Boxes.Code
FROM Warehouses RIGHT JOIN Boxes
ON Warehouses.Code = Boxes.Warehouse
WHERE Location = 'Chicago';

/* With a subquery */
SELECT Code
FROM Boxes
WHERE Warehouse IN
(
SELECT Code
FROM Warehouses
WHERE Location = 'Chicago'
);
```

11. Create a new warehouse in New York with a capacity for 3 boxes.

Click to see solution
``` INSERT
INTO Warehouses
(Location,Capacity)
VALUES ('New York',3);
```

12. Create a new box, with code "H5RT", containing "Papers" with a value of \$200, and located in warehouse 2.

Click to see solution
``` INSERT INTO Boxes
VALUES('H5RT','Papers',200,2);
```

13. Reduce the value of all boxes by 15%.

Click to see solution
``` UPDATE Boxes SET Value = Value * 0.85;
```

14. Apply a 20% value reduction to boxes with a value larger than the average value of all the boxes.

Click to see solution
```UPDATE Boxes
SET Boxes.value = Boxes.value * 0.8
WHERE Boxes.code IN
(
SELECT * FROM
(
SELECT Bx.code
FROM Boxes AS Bx
WHERE Bx.value >
(
SELECT AVG(B.value)
FROM Boxes AS B
)
) AS Bxs
);
```

15. Remove all boxes with a value lower than \$100.

Click to see solution
``` DELETE FROM Boxes WHERE Value < 100;
```

16. Remove all boxes from saturated warehouses.

Click to see solution
``` DELETE FROM Boxes
WHERE Warehouse IN
(
SELECT * FROM
(
SELECT Code
FROM Warehouses
WHERE Capacity <
(
SELECT COUNT(*)
FROM Boxes
WHERE Warehouse = Warehouses.Code
)
) AS Bxs
);
```

## Table creation code

``` CREATE TABLE Warehouses (
Code INTEGER PRIMARY KEY NOT NULL,
Location TEXT NOT NULL ,
Capacity INTEGER NOT NULL
);

CREATE TABLE Boxes (
Code TEXT PRIMARY KEY NOT NULL,
Contents TEXT NOT NULL ,
Value REAL NOT NULL ,
Warehouse INTEGER NOT NULL,
CONSTRAINT fk_Warehouses_Code FOREIGN KEY (Warehouse) REFERENCES Warehouses(Code)
);
```

Click to see MySQL syntax.
```CREATE TABLE Warehouses (
Code INTEGER NOT NULL,
Location VARCHAR(255) NOT NULL ,
Capacity INTEGER NOT NULL,
PRIMARY KEY (Code)
);
CREATE TABLE Boxes (
Code VARCHAR(255) NOT NULL,
Contents VARCHAR(255) NOT NULL ,
Value REAL NOT NULL ,
Warehouse INTEGER NOT NULL,
PRIMARY KEY (Code),
FOREIGN KEY (Warehouse) REFERENCES Warehouses(Code)
) ENGINE=INNODB;
```

## Sample dataset

``` INSERT INTO Warehouses(Code,Location,Capacity) VALUES(1,'Chicago',3);
INSERT INTO Warehouses(Code,Location,Capacity) VALUES(2,'Chicago',4);
INSERT INTO Warehouses(Code,Location,Capacity) VALUES(3,'New York',7);
INSERT INTO Warehouses(Code,Location,Capacity) VALUES(4,'Los Angeles',2);
INSERT INTO Warehouses(Code,Location,Capacity) VALUES(5,'San Francisco',8);

INSERT INTO Boxes(Code,Contents,Value,Warehouse) VALUES('0MN7','Rocks',180,3);
INSERT INTO Boxes(Code,Contents,Value,Warehouse) VALUES('4H8P','Rocks',250,1);
INSERT INTO Boxes(Code,Contents,Value,Warehouse) VALUES('4RT3','Scissors',190,4);
INSERT INTO Boxes(Code,Contents,Value,Warehouse) VALUES('7G3H','Rocks',200,1);
INSERT INTO Boxes(Code,Contents,Value,Warehouse) VALUES('8JN6','Papers',75,1);
INSERT INTO Boxes(Code,Contents,Value,Warehouse) VALUES('8Y6U','Papers',50,3);
INSERT INTO Boxes(Code,Contents,Value,Warehouse) VALUES('9J6F','Papers',175,2);
INSERT INTO Boxes(Code,Contents,Value,Warehouse) VALUES('LL08','Rocks',140,4);
INSERT INTO Boxes(Code,Contents,Value,Warehouse) VALUES('P0H6','Scissors',125,1);
INSERT INTO Boxes(Code,Contents,Value,Warehouse) VALUES('P2T6','Scissors',150,2);
INSERT INTO Boxes(Code,Contents,Value,Warehouse) VALUES('TU55','Papers',90,5);
```