1. ATS Application Programming: Java Programming
9.1 Structured Query Language (SQL)
ATS Application Programming: Java Programming

2. Objectives After completing this section, you should be able to:
Understand Structured Query Language (SQL) and its purpose
Create and execute a basic SELECT statement
Create and execute a basic INSERT statement
Create and execute a basic UPDATE statement
Create and execute a basic DELETE statement
Execute COMMIT and ROLLBACK on transaction

3. What is SQL?
SQL (Structured Query Language) is a standard interactive programming language for getting information from and updating to a database.
Statements take the form of a command language that lets you:
SELECT data
INSERT data
UPDATE data
DELETE data
Although SQL is both an ANSI and an ISO standard, many database products support SQL with proprietary extensions to the standard language.
SQL doesn’t limit itself to the four listed keywords above, it has more keywords but they are used primarily for Administrative purposes such as Create, Alter, Drop, etc.

4. Guidelines in writing SQL Statements
SQL statements are not case-sensitive
SQL statements can be on one or more lines
SQL statements are optionally ended with “;”
Keywords cannot be abbreviated or split across lines
Clauses are usually placed on separate lines
Indents are used to enhance readability
Keywords are typically entered in uppercase; all other words such as table name and columns are entered in lower case
Notes:
Some implementations require statements to be ended with “;”. An example is in using SQL in PL/SQL programming.

5. Basic SELECT Statement
Use the SELECT statement to retrieve data from one or more tables:
SELECT <column(s) >
FROM <table>
[WHERE <condition>]
[ORDER BY <column(s) [ASC|DESC]>]
table is the name of the table
column is the name of the column in the table to be selected
condition identifies the rows to be selected and is composed of column names, expressions, constraints,
sub-queries and comparison operators
column is the name of the column(s) used for sorting
(order by)
Select - CHOOSE the columns in a table that you want returned by your query
Where - FILTER the rows in a table that you want returned by your query
Order By - SORT data selected from the table in a specified order

6. Choosing Columns
To choose all the columns of the table for display, you can use the asterisk (*)
SELECT *
FROM TABLE_A
To choose specific columns on the table for display, you specify each column separated by a comma (,)
SELECT COLUMN_1,
COLUMN_2
It is best to put each column chosen in a separate line

7. Limiting Rows
The method of restriction is the basis of the WHERE clause in SQL
Character strings and dates in the WHERE clause must be enclosed in Single Quotation Marks (‘)
Numeric Values do not need the Single Quotation marks(‘)
Notes:
SQL accepts both single & double quotes but it is better to use single quotes for embedded SQL statements (i.e., inside programming codes)

8. Rows may be limited by: EQUALS CONDITION SELECT last_name, salary
Display rows based on an exact match of values.
SELECT last_name,
salary
FROM employee
WHERE salary = 30000
SELECT employee_id,
last_name
FROM employee
WHERE manager_name = ‘RAYMOND’

9. Rows may be limited by: >, < or <> CONDITION
SELECT last_name
FROM employee
WHERE salary > 30000
SELECT employee_id
FROM employee
WHERE manager_name <= ‘RAYMOND’
SELECT employee_id
FROM employee
WHERE status <> ‘ACTIVE’

10. Rows may be limited by: BETWEEN CONDITION SELECT last_name
Display rows based on a range of values
SELECT last_name
FROM employee
WHERE salary BETWEEN AND 50000
IN CONDITION
Display rows based on a list of values
SELECT employee_id
FROM employee
WHERE manager_id IN (100, 200, 300)

11. Rows may be limited by: LIKE CONDITION
Perform wildcard searches of valid search string values
Can contain either literal characters or numbers
% denotes zero or many characters
_ denotes one character
Use ESCAPE identifier to search for the actual % and _symbols. Identifies the backslash(\) as the escape character
SELECT last_name
FROM employee
WHERE last_name LIKE ‘%a’

12. Rows may be limited by: LOGICAL CONDITION SELECT last_name, job_id
AND, OR, NOT
SELECT last_name,
job_id
FROM employee
WHERE job_id NOT IN ('SSE', 'TL')
SELECT last_name,
job_id
FROM employee
WHERE salary NOT between AND 15000

13. Rows may be limited by: LOGICAL CONDITION SELECT last_name, job_id
AND, OR, NOT
SELECT last_name,
job_id
FROM employee
WHERE last_name NOT LIKE 'A%'
AND last_name NOT LIKE 'B%‘
SELECT last_name,
job_id
FROM employee
WHERE commission_pct IS NOT NULL

14. Sorting Rows ORDER BY clause ASC specifies an ascending order
DESC specifies a descending order
SELECT last_name,
salary,
job_id
FROM employee
ORDER BY salary DESC, job_id ASC
Notes:
Demo a SELECT statement from PL/SQL using HRS table
Display the result in descending order by the attribute salary. If two records have the same attribute value, the salary sorting criteria is in ascending order according to the attribute values of job_id

15. Basic INSERT Statement
INSERT INTO <table>
[ (column
[, column…] ) ]
VALUES (value
[, value…] )
table is the name of the table
column is the name of the column in the table to populate
value is the corresponding value for the column
Note: This statement with the VALUES
clause adds only one row at a time to a table.
Define INSERT

16. Basic INSERT Statement
Insert a new row containing values for each column
List values in the default order of the columns in the table
Option: list the columns in the INSERT clause
Enclose character and date values within single quotation marks
INSERT INTO departments ( department_id,
department_name, current_date)
VALUES ( 70,
‘Public Relations’,
’10-OCT-04’)

17. Inserting Rows from Another Table
Write your INSERT statement with a subquery
Do not use the VALUES clause
Match the number of columns in the INSERT clause to those in the subquery
INSERT INTO sales_reps ( id,
name,
salary)
SELECT employee_id,
last_name,
salary
FROM employees
WHERE job_id LIKE ‘%REP%’
Notes:
Demo a INSERT statement from PL/SQL using HRS table.

18. Basic UPDATE Statement
UPDATE table
SET column = value
[, column = value, …]
[WHERE condition]
table is the name of the table
column name of the column in the table to populate
value corresponding value for the column
condition identifies the rows to be updated and is
composed of column names, expressions,
constraints, sub-queries, and comparison
operators
Define UPDATE

19. Updating Rows in a Table
Specific row or rows are modified if you specify the WHERE clause
All rows in the table are modified if you omit the WHERE clause
UPDATE employees
SET department_id = 70
WHERE employee_id = 113

20. Updating Rows Based on Another Table
Use subqueries in UPDATE statements to update rows in a table based on values from another table
UPDATE copy_emp
SET department_id = (SELECT department_id
FROM employees
WHERE emp_id =100)
WHERE job_id = (SELECT job_id
WHERE emp_id = 200)
Notes:
Demo an UPDATE statement from PL/SQL using HRS table

21. Basic DELETE Statement
DELETE [FROM] table
[WHERE condition] ;
table is the name of the table
condition identifies the rows to be updated and is
composed of column names, expressions,
constraints, sub-queries, and comparison
operators
Define DELETE
NOTE: Be cautious on using this statement as this may delete all records from a table accidentally, especially without the WHERE condition.

22. Deleting Rows in a Table
A specific row or specific rows are deleted if you specify the WHERE clause
All rows in the table are deleted if you omit the WHERE clause
DELETE FROM employees
WHERE employee_id = 113 ;

23. Deleting Rows Based on Another Table
Use subqueries in DELETE statements to delete rows in a table based on values from another table
DELETE FROM employees
WHERE department_id = (SELECT department_id
FROM departments
WHERE dept_type = ‘CST’)

24. What is a Transaction?
A transaction usually means a sequence of information exchange and related work (such as database updating) that is treated as a unit for the purposes of satisfying a request and for ensuring database integrity
For a transaction to be completed and database changes to be made permanent, a transaction has to be completed in its entirety. A program that manages or oversees the sequence of events that are part of a transaction is sometimes called a transaction monitor
Transactions are supported by SQL. When a transaction completes successfully, database changes are said to be committed; when a transaction does not complete, changes are rolled back
A typical transaction is a catalog merchandise order phoned in by a customer and entered into a computer by a customer representative. The order transaction involves checking an inventory database, confirming that the item is available, placing the order and confirming that the order has been placed and noting the expected time of shipment. If we view this as a single transaction, then all of the steps must be completed before the transaction is successful and the database is actually changed to reflect the new order. If something happens before the transaction is successfully completed, any changes to the database must be documented so that they can be undone.
A transaction is a sequence of SQL statements that Oracle treats as a single unit.
Oracle recommends that you explicitly end every transaction in your application programs with a COMMIT or ROLLBACK statement, including the last transaction, before disconnecting from Oracle.
Use the COMMIT statement to end your current transaction and make permanent all changes performed in the transaction.

25. Transaction Control
Transaction Control Statements
COMMIT
ROLLBACK

26. COMMIT
Use the COMMIT statement to end your current transaction and make permanent all changes performed in the transaction
If you do not explicitly commit the transaction and the program terminates abnormally, then the last uncommitted transaction is automatically rolled back
SYNTAX:
COMMIT;
Oracle recommends that you explicitly end every transaction with a COMMIT or ROLLBACK statement before disconnecting from Oracle.

27. ROLLBACK
Use the ROLLBACK statement to undo work done in the current transaction, or to manually undo the work done by an in-doubt distributed transaction
SYNTAX:
ROLLBACK;

28. Key Points
SQL is an industry standard language for updating, and getting information from, a database
The basic and most common SQL statements are: SELECT, INSERT, UPDATE, DELETE
Transaction management is implemented in SQL using COMMIT and ROLLBACK

29. Comments & Questions
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