1. Chapter 5
Introduction to SQL

2. SQL Structured Query Language
= the “programming language” for relational databases
SQL is a nonprocedural language = the user specifies what must be done (ex. create a table), but not how it is to be done.
Several SQL dialects exist, in different RDBMSs; minor differences among them.

3. SQL – Creating DB Tables
Use CREATE TABLE command for each db table, basic syntax:
CREATE TABLE tablename (
column_1 data_type [constraints] ,
column_2 data_type [constraints], …
column_k data_type [constraints] ,
PRIMARY KEY (column_i [, column_j …]) ] );
Notes:
End each SQL command with a semicolon to execute it;
A comma separates all table element (column, PK) definitions;

4. sql.sql
CREATE TABLE users ( … first_name VARCHAR(20) NOT NULL, };

5. VARCHAR
Variable length string
Size varies from record to record.

6. create_myusers.sql sql.sql
How would you create the table in db_fall17_frank?
J:\>mysql -h cscdb.nku.edu -u frank -D db_fall17_frank -p < sql.sql
Enter password: ******

7. MySQL - SHOW and DESCRIBE
After you create the tables in your database, you can view:
All tables in the currently used database
with:
show tables;
The structure of any of the tables in the
current database with:
describe table_name;

8. myusers
J:\>mysql -h csweb.hh.nku.edu -u frank -p Enter password: ****** mysql> use db_fall17_frank; mysql> show tables; mysql> describe users;

9. SQL – Deleting DB Tables
Use DROP TABLE command for each db table you want to delete; basic syntax:
DROP TABLE tablename;
Note:
This command deletes all the rows in the table tablename and the table tablename itself!

10. DML – Adding Table Rows
SQL requires the use of the INSERT command to enter data into a table.
INSERT command’s basic syntax:
INSERT INTO tablename
VALUES (value_1, value_2, … , value_n);
This version of INSERT:
adds one table row (tuple) at a time
requires a value to be specified for every column of the table; values are specified in the same order columns were defined in

11. sql.sql INSERT INTO users …
SHA1('mypass') – 160 bit hash digest of password
NOW() – function return the current system date and time

12. INSERT Example: Notes:
insert into customers values (1, "Julie Smith", "25 Oak Street", "Airport West");
insert into orders values (NULL, 1, 49.99, " ");
Notes:
The row contents are delimited by parentheses
Attribute entries are separated by commas
String and date values must be quoted (‘ or “)
Numerical entries are not enclosed in any special characters

13. users
INSERT INTO users VALUES (NULL, ‘Charles', ‘Frank', SHA1(‘secret'), NOW());

14. SELECT
SELECT command is used to list the contents of a table (or more tables).
The simplest form (syntax) of a SELECT query is:
SELECT column_list
FROM tablename;
Column_list represents one or more attributes from tablename, separated by commas

15. SELECT SELECT name, city FROM customers;
Example:
SELECT name, city
FROM customers;
 the result contains all the rows and only the two specified columns of table customers.

16. sql.sql SELECT user_id, username FROM users;
SELECT * FROM users; Asterisk (*) can be used as a wildcard character to list all attributes for the selected rows (when column_list is *)
SELECT user_id, username FROM users;

17. Listing Table Rows
Can limit data selected by placing conditional restrictions on the rows to be included in the output → with the WHERE clause of the SELECT statement.
Syntax:
SELECT column_list FROM tablename [ WHERE condition_list ] ;
Will retrieve all the rows that match the conditions specified in the optional WHERE clause
If no rows match the specified criteria  result = an empty set of tuples (not an error!)
condition_list = one or more conditional expressions connected by logical operators

18. Listing Table Rows (cont)
WHERE clause example:
SELECT title FROM books WHERE price > 40;
Conditional restrictions in the condition_list :
column_name comparison_operator value
expression comparison_operator expression
expression – with columns and values (constants) as operands;
Comparisons include the usual “suspects”
=, !=, <, etc.
Also can use BETWEEN value1 AND value2
If a data field is empty, can test with IS NULL operator
SELECT name FROM customers WHERE address IS NULL;
 Finds records with no address specified

19. Listing Table Rows (cont)
Can match patterns with LIKE
Pattern can be simple characters up to RE
% matches any number of characters, _ matches 1 character
Can match multiple conditions using AND and OR
Can negate a condition using NOT
Example:
SELECT title
FROM books
WHERE price > 40 AND author like “Thomas%”;

20. Listing Table Rows Notes: Example:
Can sort results of query with ORDER BY:
SELECT column_list
FROM tablename
[ORDER BY column1 [ASC | DESC], column2 [ASC | DESC] …];
Notes:
Although ORDER BY produces a sorted output, the actual table contents are unaffected by the ORDER BY clause!
ORDER BY clause must be listed last in SELECT (except for LIMIT)
Example:
SELECT title, price, author FROM books ORDER BY price, author;
 all books info sorted by price and, for same price, ordered by the author
default

21. users
mysql> select * from users; mysql> select from users where last_name='Frank'; mysql> select * from users where like '%edu';

22. Updating Table Rows Use the UPDATE command to modify data in a table.
UPDATE command’s syntax:
UPDATE tablename SET column_1 = expression_1 [, column_2 = expression_2 …] [WHERE condition_list];
expression = a simple value (76 or ‘Florida’), or a formula (price – 10)
condition_list = one or more conditional expressions connected by logical operators (and, or, not)
If more than one attribute is to be updated per tuple, separate modifications with commas

23. Updating Table Rows (cont)
Examples:
UPDATE books
SET price = price * 1.1;
increase all the book prices by 10%
UPDATE customers
SET address = ‘250 Olsens Road’
WHERE customer_id = 4;
update a certain customer’s address – PK used to identify the customer
Notes:
The WHERE clause is optional
If a WHERE clause is not specified, all rows from the specified table will be modified.

24. users
mysql> select * from users; mysql> UPDATE users SET WHERE user_id = 18; mysql> select * from users where user_id='18';

25. DML – Deleting Table Rows
Use the DELETE command to delete data from a table.
DELETE command’s syntax:
DELETE FROM tablename
[WHERE condition_list ];
Notes:
WHERE clause is optional
If a WHERE clause is not specified, all rows from the specified table will be deleted

26. Deleting Table Rows (cont)
Examples:
DELETE FROM customers
WHERE customer_id = 4;
delete data about a customer who didn’t place orders for a long time
DELETE FROM books
WHERE price < 4;
delete all cheap books (none, one, or more tuples can satisfy the condition)
DELETE FROM books;
delete all books; table is not deleted, but remains empty

27. users
mysql> DELETE FROM users WHERE user_id = 8 LIMIT 1; mysql> select * from users limit 10;