15 Structured Query Language (SQL)

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

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

5 Basic SELECT Statement Use the SELECT statement to retrieve data from one or more tables: SELECT FROM [WHERE ] [ORDER BY ] tableis the name of the table columnis the name of the column in the table to be selected conditionidentifies the rows to be selected and is composed of column names, expressions, constraints, sub-queries and comparison operators columnis the name of the column(s) used for sorting (order by)

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 FROM TABLE_A 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(‘)

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

9 Rows may be limited by: >, CONDITION SELECT last_name FROM employee WHERE salary > 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 Display rows based on a range of values SELECT last_name FROM employee WHERE salary BETWEEN AND 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 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 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 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 [ (column [, column…] ) ] VALUES(value [, value…] ) tableis the name of the table columnis the name of the column in the table to populate valueis the corresponding value for the column Note: This statement with the VALUES clause adds only one row at a time to a table.

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 INTOsales_reps (id, name, salary) SELECT employee_id, last_name, salary FROMemployees WHERE job_id LIKE ‘%REP%’

18 Basic UPDATE Statement UPDATEtable SETcolumn = value [, column = value, …] [WHEREcondition] table is the name of the table columnname of the column in the table to populate valuecorresponding value for the column conditionidentifies the rows to be updated and is composed of column names, expressions, constraints, sub-queries, and comparison operators

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 SETdepartment_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 UPDATEcopy_emp SETdepartment_id = (SELECT department_id FROM employees WHERE emp_id =100) WHEREjob_id =(SELECT job_id FROM employees WHERE emp_id = 200)

21 Basic DELETE Statement DELETE[FROM] table [WHEREcondition] ; table is the name of the table conditionidentifies the rows to be updated and is composed of column names, expressions, constraints, sub-queries, and comparison operators

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 WHEREdept_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

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;

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