Chapter 7

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Chapter 7

Introduction to Structured Query Language (SQL)

Database Systems: Design, Implementation, and Management,

Seventh Edition, Rob and Coronel

Database Systems: Design, Implementation, & Management, 7 th Edition, Rob & Coronel

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In this chapter, you will learn:

• The basic commands and functions of SQL

• How to use SQL for data administration (to create tables, indexes, and views)

• How to use SQL for data manipulation (to add, modify, delete, and retrieve data)

• How to use SQL to query a database to extract useful information


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Introduction to SQL

• SQL functions fit into two broad categories:– Data definition language

• SQL includes commands to:– Create database objects, such as tables,

indexes, and views

– Define access rights to those database objects

– Data manipulation language• Includes commands to insert, update, delete,

and retrieve data within database tables


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Introduction to SQL (continued)

• SQL is relatively easy to learn

• Basic command set has vocabulary of less than 100 words

• Nonprocedural language

• American National Standards Institute (ANSI) prescribes a standard SQL

• Several SQL dialects exist


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Data Definition Commands

• Examine simple database model and database tables that will form basis for many SQL examples

• Understand data environment


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The Database Model


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The Database Model (continued)


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Creating the Database

• Following two tasks must be completed:– Create database structure – Create tables that will hold end-user data

• First task:– RDBMS creates physical files that will hold

database– Tends to differ substantially from one RDBMS

to another


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The Database Schema

• Authentication

– Process through which DBMS verifies that only registered users are able to access database

– Log on to RDBMS using user ID and password created by database administrator

• Schema– Group of database objects—such as tables

and indexes—that are related to each other


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Data Types

• Data type selection is usually dictated by nature of data and by intended use

• Pay close attention to expected use of attributes for sorting and data retrieval purposes


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Data Types (continued)


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Creating Table Structures

• Use one line per column (attribute) definition

• Use spaces to line up attribute characteristics and constraints

• Sql commands are capitalized

• NOT NULL specification

• UNIQUE specification


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Creating Table Structures (continued)

• Primary key attributes indicate both a NOT NULL and a UNIQUE specification

• RDBMS will automatically enforce referential integrity for foreign keys

• Command sequence ends with semicolon


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SQL Constraints

• NOT NULL constraint – Ensures that column does not accept nulls

• UNIQUE constraint – Ensures that all values in column are unique

• DEFAULT constraint – Assigns value to attribute when a new row is added to

table

• CHECK constraint – Validates data when attribute value is entered


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• CREATE TABLE CUSTOMER(

CUS_CODE NUMBER(7) PRIMARY KEY, CUS_LNAME VARCHAR2 (20),CUS_ZIP CHAR (5), AGENT_CODE NUMBER (3) DEFAULT

412);


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CREATE TABLE AGENT(

AGENT_CODE NUMBER(3) PRIMARY KEY,

AGENT_PHONE CHAR (10));


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CREATE TABLE Product(

p_code CHAR(10), /*...*/

p_descript VARCHAR2(35), --...

p_indate DATE,

p_onhand SMALLINT,

p_min SMALLINT,

p_price NUMBER(8,2) NOT NULL,

p_discount NUMBER(4,2),

v_code INTEGER CONSTRAINT v_code_fk

REFERENCES Vendor(v_code),

CONSTRAINT p_code_pk PRIMARY KEY (p_code));


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CREATE TABLE Product(

p_code CHAR(10) CONSTRAINT p_code_pk PRIMARY KEY,

p_descript VARCHAR2(35),

p_indate DATE,

p_onhand SMALLINT,

p_min SMALLINT,

p_price NUMBER(8,2) NOT NULL,

p_discount NUMBER(4,2),

v_code INTEGER CONSTRAINT v_code_fk

REFERENCES Vendor(v_code));


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CREATE TABLE Employee(

ssn CHAR(10),

salary NUMBER(9,2),

title VARCHAR2(20),

class NUMBER(1) constraint class_ck CHECK

(class BETWEEN 1 AND 4),

CONSTRAINT title_uk UNIQUE (title),

CONSTRAINT ssn_salary_pk PRIMARY KEY

(ssn, salary));


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SQL Indexes

• When primary key is declared, DBMS automatically creates unique index

• Often need additional indexes

• Using CREATE INDEX command, SQL indexes can be created on basis of any selected attribute

• Composite index– Index based on two or more attributes– Often used to prevent data duplication


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SQL Indexes (continued)

CREATE [UNIQUE] INDEX indexname ON tablename (column1 [, column2])

CREATE INDEX Emptest on Test (emp_num)


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SQL Indexes (continued)


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Data Manipulation Commands

• Adding table rows

• Saving table changes

• Listing table rows

• Updating table rows

• Restoring table contents

• Deleting table rows

• Inserting table rows with a select subquery


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Adding Table Rows

• INSERT – Used to enter data into table

– Insert a row each time

– Syntax: • INSERT INTO tablename

VALUES (value1, value2, … , valuen);


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Adding Table Rows (continued)

• When entering values, notice that:– Row contents are entered between parentheses– Character and date values are entered between

apostrophes– Numerical entries are not enclosed in apostrophes– Attribute entries are separated by commas– A value is required for each column

• Use NULL for unknown values


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Adding Table Rows (continued)

INSERT INTO Product VALUES (‘BRT-345’, ‘Titanium drill bit’, TO_DATE(’18-Oct-05’, ’DD-MON-YY’), 75, 10, 4.5, 0.06, NULL);

or TO_DATE (’18/Oct/05’, ’DD/MON/YY’)

or TO_DATE(’10/18/2005’, ‘MM/DD/YYYY’)

or TO_DATE(‘October 18, 2005’, ‘Month DD, YYYY’)


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Saving Table Changes

• Changes made to table contents are not physically saved on disk until, one of the following occurs:– Database is closed– Program is closed– COMMIT command is used

• Syntax:– COMMIT [WORK];

• Will permanently save any changes made to any table in the database


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Listing Table Rows

• SELECT – Used to list contents of table

– Syntax: • SELECT columnlist

FROM tablename;

• Columnlist represents one or more attributes, separated by commas

• Asterisk can be used as wildcard character to list all attributes


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Listing Table Rows (continued)

SELECT p_code, p_descript, p_indate, p_qoh, p_min, p_price, p_discount, v_code

FROM Product;

SELECT *

FROM Product;


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Listing Table Rows (continued)


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Updating Table Rows

• UPDATE – Modify data in a table

– Syntax:• UPDATE tablename

SET columnname = expression [, columname = expression][WHERE conditionlist];

• If more than one attribute is to be updated in row, separate corrections with commas


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Updating Table Rows (continued)

UPDATE Product

SET p_indate = ’18-Jan-2006’, p_price = 7.6

WHERE p_code = ‘13-Q2/P2’;


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Restoring Table Contents

• ROLLBACK– Used to restore database to its previous condition– Only applicable if COMMIT command has not been

used to permanently store changes in database

• Syntax:– ROLLBACK;

• COMMIT and ROLLBACK only work with data manipulation commands that are used to add, modify, or delete table rows


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Deleting Table Rows

• DELETE – Deletes a table row

– Syntax:• DELETE FROM tablename

[WHERE conditionlist ];

• WHERE condition is optional

• If WHERE condition is not specified, all rows from specified table will be deleted


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Deleting Table Rows (continued)

DELETE FROM Product

WHERE p_code = ‘BRT-345’;


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Inserting Table Rows with a Select Subquery

• INSERT– Inserts multiple rows from another table (source)– Uses SELECT subquery

• Query that is embedded (or nested) inside another query

• Executed first

– Syntax:• INSERT INTO tablename SELECT columnlist

FROM tablename;


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Inserting Table Rows with a Select Subquery (continued)

INSERT INTO p SELECT * from Product;

Employee(name, address, emp_num, salary)

Emp1(addr, sal, empno)

INSERT INTO Emp1

SELECT address, salary, emp_num

FROM Employee;


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Inserting Table Rows with a Select Subquery (continued)

• INSERT INTO Emp1

SELECT address, emp_num, salary

FROM Employee;

(The order of attributes matter in the above)

• INSERT INTO Emp1

SELECT * FROM Employee;

(The number of attributes are not the same!)


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Selecting Rows with Conditional Restrictions

• Select partial table contents by placing restrictions on rows to be included in output– Add conditional restrictions to SELECT

statement, using WHERE clause

• Syntax:– SELECT columnlist

FROM tablelist[ WHERE conditionlist ] ;


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Selecting Rows with Conditional Restrictions (continued)

SELECT p_descript, p_indate, p_price, v_code

FROM Product

WHERE v_code = 21344;


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FROM Product

WHERE v_code <>21344;


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SELECT p_descript, p_qoh, p_min, p_price

FROM Product

WHERE p_price <= 10;


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SELECT p_code, p_descript, p_qoh, p_min, p_price

FROM Product

WHERE p_code <= ‘1558-QW1’;


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SELECT p_descript, p_qoh, p_min, p_price, p_indate

FROM Product

WHERE p_indate >= ’20-Jan-2006’;


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SELECT p_descript, p_qoh, p_price, p_qoh*p_price

FROM Product;


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SELECT p_descript, p_qoh, p_price, p_qoh*p_price AS totalvalue

FROM Product;


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Arithmetic Operators: The Rule of Precedence

• Perform operations within parentheses

• Perform power operations

• Perform multiplications and divisions

• Perform additions and subtractions


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Arithmetic Operators: The Rule of Precedence (continued)


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Logical Operators:AND, OR, and NOT


FROM Product

WHERE v_code = 21344 OR v_code = 24288;


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Logical Operators:AND, OR, and NOT (continued)


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FROM Product

WHERE p_price < 50 AND p_indate > ’15-Jan-2006’;


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FROM product

WHERE (p_price < 50 AND p_indate > ’15-Jan-2006’) OR v_code = 24288;


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Special Operators

• BETWEEN– Used to check whether attribute value is within

a range

• IS NULL– Used to check whether attribute value is null

• LIKE– Used to check whether attribute value

matches given string pattern


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Special Operators (continued)

• IN– Used to check whether attribute value

matches any value within a value list

• EXISTS– Used to check if subquery returns any rows


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• SELECT *

FROM Product

WHERE p_price BETWEEN 50.00 AND 100.00;

• SELECT *

FROM product

WHERE p_price > 50.00 AND p_price<100.00;

• SELECT p_code, p_descript, v_code

FROM Product

WHERE v_code IS NULL;


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• The LIKE special operator is used in conjunction with wildcards to find patterns within string attributes.– % means any and all following characters are eligible.

For example,

‘J%’ includes Johnson, Jones, July, etc.

‘Jo%’ includes Johnson, Jones, etc.

– _ means any one character may be substituted for the underscore. For example,

‘_o_es’ includes Jones, Cones, Cokes, totes, ets.


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• SELECT v_name, v_contact, v_areacode

FROM Vendor

WHERE v_contact LIKE ‘Smith%’;


FROM Vendor

WHERE UPPER(v_contact) LIKE ‘SMITH%’;


FROM Vendor

WHERE v_contact NOT LIKE ‘Smith%’;


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• SELECT *

FROM Product

WHERE v_code IN (21344, 24288);

• SELECT v_code, v_name

FROM Vendor

WHERE v_code IN (SELECT v_code FROM Product);

• SELECT *

FROM Vendor

WHERE v_code EXIST (SELECT *

FROM Product

WHERE p_qoh <= p_min);


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Advanced Data Definition Commands

• All changes in table structure are made by using ALTER command– Followed by keyword that produces specific

change

– Following three options are available:• ADD• MODIFY• DROP


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Changing a Column’s Data Type

• ALTER can be used to change data type

• Some RDBMSs (such as Oracle) do not permit changes to data types unless column to be changed is empty


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Changing a Column’s Data Characteristics

• Use ALTER to change data characteristics

• If column to be changed already contains data, changes in column’s characteristics are permitted if those changes do not alter the data type


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Adding a Column

• Use ALTER to add/modify column

ALTER TABLE Customer

ADD address VARCHAR2(20);

ALTER TABLE Customer

MODIFY balance NUMBER(8,2);


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Dropping a Column

• Use ALTER to drop column– Some RDBMSs impose restrictions on the

deletion of an attribute

ALTER TABLE Product

DROP CONSTRAINT v_code_fk;


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Dropping a Column (continued)

• UPDATE Product

SET p_salecode = ‘2’

WHERE p_code = ‘1546-QQ2’;

• UPDATE Product


WHERE p_code = ‘1546-QQ2’ OR p_code = ‘2232/QTY’;

• UPDATE Product


WHERE p_indate < ’25-Dec-2005’;


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Advanced Data Updates


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Copying Parts of Tables

• SQL permits copying contents of selected table columns so that the data need not be reentered manually into newly created table(s)

• First create the PART table structure

• Next add rows to new PART table using PRODUCT table rows


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Copying Parts of Tables (continued)

• CREATE TABLE Part AS

SELECT p_code AS part_code, p_descript AS part_descript, p_price AS part_price, v_code

FROM Product;


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Copying Parts of Tables (continued)


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Adding Primary and Foreign Key Designations

• When table is copied, integrity rules do not copy, so primary and foreign keys need to be manually defined on new table

• User ALTER TABLE command– Syntax:

• ALTER TABLE tablename ADD PRIMARY KEY(fieldname);

• For foreign key, use FOREIGN KEY in place of PRIMARY KEY


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Deleting a Table from the Database

• DROP– Deletes table from database

– Syntax:• DROP TABLE tablename;


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Advanced Select Queries

• SQL provides useful functions that can:– Count

– Find minimum and maximum values

– Calculate averages

• SQL allows user to limit queries to only those entries having no duplicates or entries whose duplicates may be grouped


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Ordering a Listing (continued)

• SELECT p_code, p_descript, p_indate, p_price

FROM Product

ORDER BY p_price;

• SELECT p_code, p_descript, p_indate, p_price

FROM Product

ORDER BY p_price DESC;

• SELECT emp_lname, emp_fname, emp_initial, emp_areacode,

emp_phone

FROM Employee

ORDER BY emp_lname, emp_fname, emp_initial;


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Ordering a Listing


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• SELECT p_descript, v_code, p_indate,

p_price

FROM Product

WHERE p_indate < ’21-Jan-2006’ AND

p_price <= 50.00

ORDER BY v_code, p_price DESC;


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Listing Unique Values (continued)

• SELECT DISTINCT v_code

FROM Product;


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Listing Unique Values


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Aggregate Functions


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Aggregate Functions (continued)


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Grouping Data


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Grouping Data (continued)


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Grouping Data (continued)


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Virtual Tables: Creating a View

• View is virtual table based on SELECT query– Can contain columns, computed columns,

aliases, and aggregate functions from one or more tables

• Base tables are tables on which view is based

• Create view by using CREATE VIEW command


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Virtual Tables: Creating a View (continued)


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Joining Database Tables

• Ability to combine (join) tables on common attributes is most important distinction between relational database and other databases

• Join is performed when data are retrieved from more than one table at a time

• Join is generally composed of an equality comparison between foreign key and primary key of related tables


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Joining Database Tables (continued)


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• SLECT p_descript, p_price, v_name,

v_contact, v_areacode, v_phone

FROM Product, Vendor

WHERE product.v_code = vendor.v_code;


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• SLECT p_descript, p_price, v_name,

v_contact, v_areacode, v_phone

FROM Product, Vendor

WHERE product.v_code = vendor.v_code AND p_indate > ’15-Jan-2006’;


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Joining Tables with an Alias

• Alias can be used to identify source table

• Any legal table name can be used as alias

• Add alias after table name in FROM clause– FROM tablename alias


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Recursive Joins


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Recursive Joins (continued)

• SELECT E.emp_mgr, E.emp_lname, M.emp_num, E.emp_lname

FROM Emp E, Emp M

WHERE E.emp_mgr = M.emp_num

ORDER BY E.emp_mgr;


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Recursive Joins (continued)


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Outer Joins

• SELECT p_code, V.v_code, v_name

FROM product P, vendor V

WHERE V.v_code = P.v_code(+);

• SELECT p_code, V.v_code, v_name

FROM product P, vendor V

WHERE P.v_code = V.v_code(+);


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Left Outer Joins


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Right Outer Joins (continued)


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Grant and Revoke Privileges on Tables

• Security is an issue in the access of a table from a foreign account.

• The creator of the table has no restriction on access and may or may not pass along manipulation privileges to others.

GRANT {priv | ALL}

ON table-name

TO {specific user | PUBLIC};


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GRANT SELECT, INSERT

ON Customer

TO fred, mary, joe;

GRANT ALL GRANT SELECT

ON Customer ON Customer

TO fred; TO PUBLIC;


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SELECT *

FROM mary.Customer;

REVOKE SELECT

ON Customer

FROM PUBLIC;


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Exercises

1. Student(stno, sname)

Grade_report(student_number,

course_no,grade)

(1) List the names of students who have earned

A’s or B’s in any course?

(2)List the names and grades of all students who have earned A’s or B’s in any course?


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Exercises

Course(course_number, credit_hours, course_name, offering_dept)

Department(dept_code, dept_name)

Find the names of all departments that offer a course with “INTRO” in the title)


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Exercises

Student(stno, sname, major, class)

Grade_report(student_number, section_id,

grade)

Section(section_id, course_num, semester,

year, instructor, bldg, room)

List the student name, student major code, and section identifier of students who earned C’s in courses taught by Professor Johns (JOHNS)?


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Exercises

Room(room_id, capacity)

List all room have a below-average capacity?


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Exercises

SAILORS(S_ID, S_NAME, S_RATING, S_AGE)

BOATS(B_ID, B_NAME, B_COLOR)

RESERVES(S_ID, B_ID, R_DAY)

A. Find all sailors with a rating above 7.

B. Find the name of sailors who have reserved a red or a green boat.

C. Find the name of sailors who are older than the oldest sailors with a rating of 10.


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Nulls Revisited

Name Salary

Joe 1000

Sam 2000

Bill 3000

Dave

SELECT count(*), avg(salary), sum(salary),

max(salary), min(salary)

FROM


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Nulls Revisited

Name Salary

Joe 1000

Sam 2000

Bill 3000

Dave

SELECT count(*), avg(salary), sum(salary),

max(salary), min(salary)

FROM Sal;


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Nulls Revisited

count(*) avg sum min max

4 2000 6000 1000 3000

Select avg(NVL(salary, 0))

from Sal;

AVG(NVL(SALARY, 0))

1500


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Delete and Referential Constraint

• On Delete Restrict– Default referential integrity delete option, which is not

explicitly allowed in Oracle.

• On Delete Cascade (dangerous!)

Create table employee

( empno number (3) primary key,

empname varchar2(20),

dept number(3) references

department(deptno) on delete cascade);


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Delete and Referential Constraint

• On Delete Set NULL

Create table Employee

( empno number (3) primary key,

empname varchar2(20),

dept number(3) references

Department(deptno) on delete set

NULL);


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Summary

• SQL commands can be divided into two overall categories: – Data definition language commands

– Data manipulation language commands

• The ANSI standard data types are supported by all RDBMS vendors in different ways

• Basic data definition commands allow you to create tables, indexes, and views


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Summary (continued)

• DML commands allow you to add, modify, and delete rows from tables

• The basic DML commands are SELECT, INSERT, UPDATE, DELETE, COMMIT, and ROLLBACK

• INSERT command is used to add new rows to tables

• SELECT statement is main data retrieval command in SQL


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Summary (continued)

• Many SQL constraints can be used with columns

• The column list represents one or more column names separated by commas

• WHERE clause can be used with SELECT, UPDATE, and DELETE statements to restrict rows affected by the DDL command


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Summary (continued)

• Aggregate functions– Special functions that perform arithmetic

computations over a set of rows

• ORDER BY clause– Used to sort output of SELECT statement– Can sort by one or more columns and use

either an ascending or descending order

• Join output of multiple tables with SELECT statement


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Summary (continued)

• Natural join uses join condition to match only rows with equal values in specified columns

• Right outer join and left outer join used to select rows that have no matching values in other related table

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Chapter 7