1. CHAPTER 7 DATABASE ACCESS THROUGH WEB
PART 2 OF 2
[Structured Query Language]
Madam Hazwani binti Rahmat

2. WHAT IS SQL? SQL stands for Structured Query Language.
It is pronounced as “SQL” or “sequel.
SQL is a query language used for accessing and modifying information in the database.
Although SQL is an ANSI (American National Standards Institute) standard, there are many different versions of the SQL language.
However, to be compliant with the ANSI standard, all SQL versions support at least the major commands (such as SELECT, UPDATE, DELETE, INSERT, WHERE) in a similar manner.

3. SQL STATEMENTS SQL is not case sensitive.
It is a simple language with a limited number of commands and those commands are very readable and are almost structured like English sentences.
Semicolon is the standard way to separate each SQL command in database systems that allow more than one SQL statement to be executed in the same call to the server. Some database systems require a semicolon at the end of each SQL statement.
MS Access and SQL Server 2000 and do not require a semicolon after each SQL statement, but some database programs force it.

4. SQL DML AND DDL SQL can be divided into TWO parts:
Data Manipulation Language (DML)
DML refers to the query and update commands.
It is used to insert, select, update, and delete records in the database.
Basic DML commands are:
SELECT - Retrieves data from the database
INSERT - Inserts new data into the database
UPDATE - Updates existing data in the database
DELETE - Deletes existing data from the database

5. SQL DML AND DDL Data Definition Language (DDL)
The DDL part of SQL permits database tables to be created or deleted.
The most important DDL statements in SQL are:
CREATE DATABASE - creates a new database
ALTER DATABASE - modifies a database
CREATE TABLE - creates a new table
ALTER TABLE - modifies a table
DROP TABLE - deletes a table
CREATE INDEX - creates an index (search key)
DROP INDEX - deletes an index

6. SQL SELECT STATEMENT
The SELECT statement is used to select data from a database.
The SELECT statement returned ALL the results from the queried database table.
A simple SQL SELECT Statement, requires :
Column(s) Name
The columns that will be returned in the results.
Table Name.
The table that will be queried to retrieve the desired results.

7. SQL SELECT STATEMENT Syntax (To select one / more columns) :
SELECT column_name FROM table_name
Example :
SELECT firstName, age FROM employee
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
firstName
age
Alex 28
Billy 40
Craig 35
Original Data : Table employee
Query Result

8. SQL SELECT STATEMENT Syntax (To select ALL columns) :
SELECT * FROM table_name
Example :
SELECT * FROM employee
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
Original Data : Table employee
Query Result

9. SQL WHERE CLAUSE
The WHERE clause not only used in SELECT statement, but it is also used in UPDATE, DELETE statement etc.
The WHERE clause is used to FILTER records that satisfy a given condition.
The WHERE clause returned MATCHING results from the queried database table restricted to a specific condition.
“condition” is the filter to be applied on the results. The filter could be a range, single value or sub query.

10. SQL WHERE CLAUSE Syntax (applicable for one / more columns) :
SELECT column_name FROM table_name
WHERE column_name = ‘criteria’
SQL uses single quotes around text values (most database systems will also accept double quotes).
However, numeric values should not be enclosed in quotes.

11. SQL WHERE CLAUSE Example (for text values):
SELECT firstName,lastName FROM employee
WHERE lastName = ‘James’
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
firstName
lastName
Alex
James
Billy
Original Data : Table employee
Query Result

12. SQL WHERE CLAUSE Example (for numeric values):
SELECT firstName,lastName FROM employee
WHERE age= 28
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
firstName
lastName
Alex
James
Original Data : Table employee
Query Result

13. SQL AND , OR & NOT
The WHERE clause can filter records based on more than one condition using operators.
With the WHERE clause, the following operators can be used:
Operator
Description =
Equal
<> or !=
Not equal
>
Greater than
<
Less than
>=
Greater than or equal
LIKE
Search for a pattern

14. SQL AND , OR & NOT
The AND operator can be used to join two or more conditions in the WHERE clause.
Both sides of the AND condition must be true in order for the condition to be met and for those rows to be displayed.
Syntax (applicable for one / more columns) :
SELECT column_name FROM table_name
WHERE condition1 AND condition_N
both conditions must be TRUE

15. SQL AND , OR & NOT Example (applicable for one / more columns) :
SELECT empID, firstName, age FROM employee
WHERE lastName = ‘James’ AND age > 20
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
empID
firstName
age 1
Alex 28 2
Billy 40
Original Data : Table employee
Query Result

16. SQL AND , OR & NOT
The OR operator can be used to join TWO or more conditions in the WHERE clause also.
However, either or both side of the OR operator can be true and the condition will be met - hence, the rows will be displayed.
Syntax (applicable for one / more columns) :
SELECT column_name FROM table_name
WHERE condition1 OR condition_N
either or both conditions can be TRUE

17. SQL AND , OR & NOT Example (applicable for one / more columns) :
SELECT empID, firstName, age FROM employee
WHERE firstName = ‘Alex’ OR lastName = ‘Dave’
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
empID
firstName
age 1
Alex 28 3
Craig 35
Original Data : Table employee
Query Result

18. SQL AND , OR & NOT
You can also combine AND and OR (use parenthesis to form complex expressions).
Syntax (applicable for one / more columns) :
SELECT column_name FROM table_name
WHERE condition1 AND
(condition_X OR condition_Y )

19. SQL AND , OR & NOT Example (applicable for one / more columns) :
SELECT empID, firstName, age FROM employee
WHERE age < 40 AND
(firstName = ‘Alex’ OR lastName = ‘James’ )
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
empID
firstName
age 1
Alex 28
Original Data : Table employee
Query Result

20. SQL AND , OR & NOT
To find rows that do not satisfy a condition, the logical operator, NOT can be used.
If a condition is satisfied, then the row is not returned.
Syntax (applicable for one / more columns) :
SELECT column_name FROM table_name
WHERE NOT condition

21. SQL AND , OR & NOT Example (applicable for one / more columns) :
SELECT empID, firstName, age FROM employee
WHERE NOT lastName = ‘James’
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
empID
firstName
age 3
Craig 35
Original Data : Table employee
Query Result

22. SQL LIKE
The LIKE operator is used in a WHERE clause to search for a specified pattern in a column.
The LIKE pattern matching operator can also be used in the conditional selection of the WHERE clause.
LIKE is a very powerful operator that allows to select only rows that are "like" what specified.
The percent sign "%" can be used as a wildcard to match any possible character that might appear before or after the characters specified.

23. SQL LIKE Syntax(applicable for one / more columns) :
SELECT column_name FROM table_name
WHERE column_name LIKE pattern
Example(applicable for one / more columns) :
SELECT empID, lastName, age FROM employee
WHERE lastName LIKE ‘%a%’
empID
lastName
age 1
James 28 2 40 3
Dave 35
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
Query Result
Original Data : Table employee

24. SQL DISTINCT
In a table, some of the columns may contain duplicate values. This is not a problem, however, sometimes there is a need to list only the different (distinct) values in a table.
The DISTINCT keyword can be used to return only distinct (different) values.
The SQL DISTINCT keyword is used in conjunction with SELECT statement to eliminate all the duplicate records and fetching only unique records.

25. SQL DISTINCT Syntax: Example: Query Result
SELECT DISTINCT column_name FROM table_name
Example:
SELECT DISTINCT lastName FROM employee
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
lastName
James
Query Result
Original Data : Table employee

26. SQL JOIN
The JOIN keyword is used in an SQL statement to query data from TWO or more tables, based on a relationship between certain columns in these tables.
Tables in a database are often related to each other with keys.

27. SQL JOIN Syntax(applicable for one / more columns) :
SELECT column_name FROM table_name1
INNER JOIN table_name2
ON table_name1.PK = table_name2.FK
The INNER JOIN keyword returns rows when there is at least one match in both tables.
If there are rows in table1 that do not have matches in table 2, those rows will NOT be listed.

28. SQL JOIN Example (applicable for one / more columns) : Query Result
SELECT firstname, department.division FROM employee
INNER JOIN department
ON employee.empID = department.empID
firstName
division
empID
Alex
Sales 1
Billy
Marketing 2
Craig HR 3
Query Result
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
deptID
division
empID 1 HR 3 2
Sales
Marketing
Original Data : Table1 : employee
Original Data : Table2 : department

29. SQL ORDER BY
The ORDER BY keyword is used to sort the query result by a specified column.
Syntax(sort by one column) :
SELECT * FROM table_name
ORDER BY column_name
Example (sort by one column) :
SELECT * FROM employee
ORDER BY firstName
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
Original Data : employee
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
Query Result

30. SQL ORDER BY Syntax(sort by multiple column) :
SELECT * FROM table_name
ORDER BY column_name1,
column_name_n
Example (sort by multiple column) :
SELECT * FROM employee
ORDER BY firstName, lastName
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
Original Data : employee
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
Query Result

31. SQL ORDER BY DESC
The ORDER BY keyword sorts the records in ascending order by default.
Syntax(sort by one column) :
SELECT * FROM table_name
ORDER BY column_name1
DESC
Example (sort by one column) :
SELECT * FROM employee
ORDER BY age
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
Original Data : employee
empID
firstName
lastName
age 2
Billy
James 40 3
Craig
Dave 35 1
Alex 28
Query Result

32. SQL INSERT
The INSERT INTO statement is used to insert a new record in a table.
Syntax(all column) :
INSERT INTO table_name
VALUES (value1, value2, value_n)
Syntax(certain column) :
INSERT INTO table_name (column1, column2, column_n)
When adding a new row, ensure the data type of the value and the column matches and follow the integrity constraints, if any, defined for the table.

33. SQL INSERT Example(all column) : Original Data : employee Query Result
INSERT INTO employee
VALUES (4, ‘Matt’, ‘Kent’, 30)
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35 4
Matt
Kent 30
Original Data : employee
Query Result

34. SQL INSERT Example(all column) : Original Data : employee Query Result
INSERT INTO employee (empID, firstName, lastName)
VALUES (5, ‘Henry’, ‘Owen’)
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35 4
Matt
Kent 30
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35 4
Matt
Kent 30 5
Henry
Owen
Original Data : employee
Query Result

35. SQL UPDATE
The UPDATE statement is used to update existing records in a table.
Syntax(all column) :
UPDATE table_name
SET column1=value1, column1=value1, column_n=value_n
WHERE columnX=valueX
The WHERE clause specifies which record or records that should be updated. If it is omitted, all records will be updated.

36. SQL UPDATE Example(all column) : Query Result Original Data : employee
UPDATE employee
SET age=29
WHERE empID=5
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35 4
Matt
Kent 30 5
Henry
Owen
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35 4
Matt
Kent 30 5
Henry
Owen 29
Query Result
Original Data : employee

37. SQL DELETE The DELETE statement is used to delete records in a table.
Syntax(one record) :
DELETE FROM table_name
WHERE columnX=valueX
It is possible to delete all rows in a table without deleting the table. This means that the table structure, attributes, and indexes will be intact:
Syntax(all records) :
DELETE FROM table_name or
DELETE * FROM table_name

38. SQL DELETE Example(all column) : Original Data : employee Query Result
DELETE FROM employee
WHERE empID=4
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35 4
Matt
Kent 30
empID
firstName
lastName
age 1
Alex
James 28 2
Billy 40 3
Craig
Dave 35
Original Data : employee
Query Result