Chapter 7 - Structured Query Language (SQL)
Note I
Primary Chapter Objectives
To learn
 The basic commands and functions of SQL
 How SQL is used for data administration (to create tables, indexes, and views)
 How SQL is used for data manipulation (to add, modify, delete, and retrieve data: INSERT,
UPDATE, and DELETE, SELECT)
 How to use SQL to query a database to extract useful information
 About more advanced SQL features such as updatable views, stored procedures, and triggers
1. Introduction
SQL is considered to be a 4GL. A Fourth Generation Language (4GL) is a nonprocedural
language. That is, its user merely commands what is to be done without having to worry
about how it's to be done. Contrast this approach to that taken by such 3GL languages as
COBOL, BASIC, or Pascal. Given this characteristic, the 4GL languages are much easier to
use than their 3GL predecessors.
Two sub types of SQL
- Data definition(DDL) creates the database and its table structures (code that works with
metadata)
- Data manipulation(DML) selects, deletes and updates data within the database tables
(code that works with actual data)
- .
Three basic data functions are provided by SQL:
 Data definition through the use of CREATE - DDL
 Data manipulation using INSERT, UPDATE, and DELETE - DML
 Data querying through the use of SELECT - DML ... which is the basis for all SQL
queries.
2. Data definition commands
DDL allows specification of not only a set of relations (tables) but also information about
each relation, including
- CREATE SCHEMA - The schema for each database
- CREATE TABLE – creates each table within a database
Integrity constraints.
- The set of indices to be maintained for each relation.
- Security and authorization information for each relation
- The physical storage structure of each relation on disk.
 Schemas – a group of related database objects such as tables and indexes owned by a specific
user (usually the creator)
Syntax:
CREATE SCHEMA CUSTOMER_IS
Tables are then stored as schema_name.table_name
With Oracle: if a schema name is not supplied, the default schema name is the
username of the creator.
Example: CSC30501.EMP_TBL
 Creating table structures
Syntax:
CREATE TABLE <table name> (
attribute_1_name and characteristics,
attribute_2_name and characteristics,
attribute_3_name and characteristics,
primary key designation,
foreign key designation and foreign key requirements ) ;
Data Types supported:
Character:
char(n) - fixed length character string with user specified length n (n <=255)
Oracle = 1 – 2,000 characters
varchar(n) - variable length character strings, with user-specified maximum length n.
Oracle = VARCHAR2 – up to 4,000 characters
Numeric:
NUMBER(l,d) - fixed point number, with user-specified precision of digits,
with d digits to the right of decimal point. If no digits specified,
Oracle will assume NO decimal points in number
DECIMAL(l,d)
INTEGER – Up to 11 digits.
SMALLINT – integer values up to six digits.
Date:
DATE – stores dates in the Julian format. The year value is four digits long (0001- 9999),
month two digits (01-12). Day two digits 01 – 31
Oracle date: DD-MON-YY example: 09-Oct-03
Example 1: VENDOR, PRODUCT
CREATE TABLE VENDOR
(V_CODE
INTEGER
V_NAME
VARCHAR2(35)
V_CONTACT
VARCHAR2(15)
V_AREACODE
CHAR(3)
V_PHONE
CHAR(7)
V_STATE
CHAR(2)
V_ORDER
CHAR(5)
PRIMARY KEY (V_CODE));
NOT
NOT
NOT
NOT
NOT
NOT
NOT
NULL
NULL,
NULL,
NULL,
NULL,
NULL,
NULL,
UNIQUE,
CREATE TABLE PRODUCT(
P_CODE
VARCHAR(10)
NOT NULL
P_DESCRIPT
VARCHAR(35)
NOT NULL,
P_INDATE
DATE
NOT NULL,
P_ONHAND
SMALLINT
NOT NULL,
P_MIN
SMALLINT
NOT NULL,
P_PRICE
DECIMAL(8,2)
NOT NULL,
P_DISCOUNT
DECIMAL(4,1)
NOT NULL,
V_CODE
INTEGER,
PRIMARY KEY (P_CODE),
FOREIGN KEY (V_CODE) REFERENCES VENDOR
ON DELETE RESTRICT
ON UPDATE CASCADE);
UNIQUE,
 The list of attributes is enclosed in parentheses. A comma is used after each attribute and
its characteristics have been defined.
 If the primary key is a composite key, all of its components are contained within the
parentheses and are separated with commas. The order of the primary components is
important since the indexing starts with the first-mentioned attribute, then proceeds with
the next attribute, and so on.
Example 2:
CREATE TABLE BRANCH(
Optional in Oracle
BRANCH_NAME
CHAR(15) NOT NULL UNIQUE,
BRANCH_CITY
CHAR(30),
ASSETS
INTEGER,
SQL integrity constraints
PRIMARY KEY (BRANCH_NAME),
CHECK (ASSETS >=0 ));

Delete a table from the database: DROP <table name>;
DROP TABLE BRANCH;

SQL Integrity Constraints
o Adherence to entity integrity and referential integrity rules is crucial
o Entity integrity is enforced automatically if the primary key specified in the
CREATE TABLE command sequence exists
o
o
Referential integrity can be enforced with the specification of FOREIGN KEY
Other specifications to ensure conditions met:
 ON DELETE RESTRICT
 Example: cannot delete a vendor record if a product references
that vendor
 ON UPDATE CASCADE
 Example: if a change is made to the vendor code of a specific
record, a change will automatically occur to that vendor code on
the product table
(In Oracle, it’s not necessary to include the ON DELETE RESTRICT and ON
UPDATE CASCADE constraints in the table definition because the DBMS
automatically enforces those constraints when a foreign key is defined
Also, in Oracle. it is not necessary to include NOT NULL or UNIQUE on the
primary key)



Using Domains
Domain is set of permissible values for a column
Definition requires:
 Name
 Data type
 Default value
 Domain constraint or condition
CREATE DOMAIN <domain_name> AS DATA_TYPE
[DEFAULT <default_value>]
[CHECK (<condition>)]
Example:
CREATE DOMAIN MARITAL_STATUS AS VARCHAR(8)
CHECK (VALUE IN (‘Single’, ‘Married’, ‘Divorced’, ‘Widowed’));
We can use the domain name instead of the attribute’s data type in the CREATE TABLE
command.
CREATE TABLE EMPLOYEE (
EMP_NUM
EMP_LNAME
EMP_FNAME
EMP_STATUS
INTEGER ,
VARCHAR(15)
VARCHAR(15)
MARITAL_STATUS
NOT NULL,
NOT NULL,
NOT NULL);
To delete a domain definition, use
DROP DOMAIN <domain_name> [RESTRICT | CASCADE]
Example: DROP DOMAIN MARITAL_STATUS CASCADE;
DROP TABLE vendor;

Save the tables:
Eg. COMMIT PRODUCT;
COMMIT <table name>;
o Any changes made to the table contents are not physically saved on disk until
you use the COMMIT command, close the table, or log out SQL.
o Do not X out of the software, any changes you made will NOT be committed
to the database.
o It’s used to save additions, changes, and deletions made in the table contents.
The ultimate purpose of the COMMIT and ROLLBACK commands is to ensure
database update integrity in transaction management