1. SQL Data Definition II Stanislava Armstrong http://www.cs.nott.ac.uk/~saw/teaching/G64DBS/lecture_slides.html 1SQL Data Definition II

2. Creating Tables From last lecture… – CREATE TABLE – Columns Data types [NOT] NULL, DEFAULT values – Constraints Primary keys Unique columns Foreign keys CREATE TABLE (, :, : )[Engine = ]; 2SQL Data Definition II

3. Deleting Tables To delete a table use: DROP TABLE [IF EXISTS] e.g.: DROP TABLE Fruit; BE CAREFUL with any SQL statement with DROP in it – You will delete any information in the table as well – You won’t normally be asked to confirm – There is no easy way to undo the changes 3SQL Data Definition II

4. Changing Tables Sometimes you want to change the structure of an existing table – One way is to DROP it then rebuild it – This is dangerous, so there is the ALTER TABLE command instead ALTER TABLE can – Add a new column – Remove an existing column – Add a new constraint – Remove an existing constraint – Change a column’s name and definition 4SQL Data Definition II

5. ALTERing Columns I To add columns use: ALTER TABLE ADD COLUMN ; To remove columns use: ALTER TABLE DROP COLUMN ; E.g.: #add a Quality column to the Fruit table ALTER TABLE Fruit ADD COLUMN Quality int; #remove the Quality column from the Fruit table ALTER TABLE Fruit DROP COLUMN Quality; 5SQL Data Definition II

6. ALTERing Columns II To change columns use: ALTER TABLE CHANGE COLUMN ; To modify a column’s definition use: ALTER TABLE MODIFY COLUMN ; 6SQL Data Definition II The new column definitions have to be compatible with all values already entered into the column.

7. ALTERing Constraints To add constraints use: ALTER TABLE ADD CONSTRAINT ; To remove UNIQUE constraints use: ALTER TABLE DROP INDEX ; To remove any other constraints use: ALTER TABLE DROP CONSTRAINT ; Examples: #make the fruitName column in the Fruit table UNIQUE ALTER TABLE Fruit ADD CONSTRAINT unFruitName UNIQUE (fruitName); #remove the UNIQUE constraint on fruitName column ALTER TABLE Fruit DROP INDEX unFruitName; 7SQL Data Definition II

8. INSERT, UPDATE, DELETE INSERT - add a row to a table UPDATE - change row(s) in a table DELETE - remove row(s) from a table UPDATE and DELETE use ‘ WHERE clauses’ to specify which rows to change or remove BE CAREFUL with these - an incorrect WHERE clause can destroy lots of data 8SQL Data Definition II

9. INSERT INSERT INTO [(col1, col2, …)] VALUES (val1, val2, …); e.g.: INSERT INTO Fruit (FruitID, FruitName, FruitPrice) VALUES (NULL, 'kiwi', 20); – The number of columns and values must be the same – If you are adding a value to every column, you don’t have to list them, but you will need to put them in the correct order 9SQL Data Definition II

10. INSERT Fruit ID 1 Name kiwi Price 20 Fruit ID 1 2 Name kiwi apple Price 20 Fruit ID 1 2 Name kiwi apple Price 20 34 Fruit ID 1 2 Name kiwi apple Price 20 34 INSERT INTO Fruit (ID, Name, Price) VALUES (2, ‘apple’, 34) INSERT INTO Fruit (Name, ID) VALUES (‘apple’, 2) INSERT INTO Fruit VALUES (2, ‘apple’, 34) 10SQL Data Definition II

11. UPDATE SET col1 = val1 [,col2 = val2…] [WHERE ]; e.g.: UPDATE Fruit SET FruitID = 5 WHERE FruitName = 'kiwi‘; – All rows where the condition is true have the columns set to the given values – If no condition is given all rows are changed so BE CAREFUL – Values are constants or can be computed from columns – You can update multiple tables at the same time 11SQL Data Definition II

12. UPDATE Fruit ID 1 2 3 4 Name kiwi apple grape lemon Price 20 34 70 2 UPDATE Fruit SET Price = 100, Name = ‘melon’ WHERE ID = 4; 12SQL Data Definition II Fruit ID 1 2 3 4 Name kiwi apple grape melon Price 20 34 70 100 Fruit ID 1 2 3 4 Name kiwi apple grape lemon Price 25 39 75 7 UPDATE Fruit SET Price = Price +5;

13. DELETE Removes all rows which satisfy the condition DELETE FROM [WHERE ]; – If no condition is given then ALL rows are deleted - BE CAREFUL – Some versions of SQL also have TRUNCATE TABLE which is like DELETE FROM but it is quicker as it doesn’t record its actions e.g.: DELETE FROM Fruit WHERE Price > 30; 13SQL Data Definition II

14. DELETE Fruit IDNamePrice DELETE FROM Fruit; or TRUNCATE TABLE Fruit; DELETE FROM Fruit WHERE Price = 20; 14SQL Data Definition II Fruit ID 1 2 3 4 Name kiwi apple grape lemon Price 20 34 70 20 Fruit ID 2 3 Name apple grape Price 34 70

15. Being Careful When using DELETE and UPDATE – You need to be careful to have the right WHERE clause – You can check it by running a SELECT statement with the same WHERE clause first (more on this later :) Before running DELETE FROM Student WHERE Year = 3; run SELECT * FROM Student WHERE Year = 3; 15SQL Data Definition II

16. Exercise 16SQL Data Definition II

17. Exercise -Sam brought a holiday to Varna and is leaving on 23 rd August 2012. He told us that lives in Chilwell, but he hasn’t given us a phone number. Update the database to reflect the new booking. -Tania hasn’t sent us the payment for the holiday, her address is too vague and we haven’t been able to get hold of her over the phone. Remove her booking. -Add £10.50 to the price of all holidays that cost more than £200.00. -Add a new column, Attractions, to the Destination table. This column should hold a string of up to 500 characters, and if no Attractions is provided then it should default to the empty string. 17SQL Data Definition II

18. Reading Material The Manga Guide to Databases – chapters 3 Database Systems – A Practical Approach to Design, Implementation and Management by Connolly and Begg – chapters 5 and 6 Any other book – chapter on SQL data definition http://dev.mysql.com/doc/refman/5.1/en/sql- syntax-data-definition.html- MySQL documentation for data definition http://dev.mysql.com/doc/refman/5.1/en/sql- syntax-data-definition.html SQL Data Definition18