Introduction to SQL
Outline
Overview of Structured Query language
(SQL)
Components of SQL
DDL Commands: Basics
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SQL: Overview
Pronunciation: “S-Q-L” or “Sequel”
Stands for: Structured Query Language
SQL has become the de facto standard
language for creating and querying relational
databases
SQL has been implemented in various
platforms that include mainframe and personal
computer systems
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SQL Standard: Purposes
Specify the syntax and semantics of SQL
data definition and manipulation
languages
– Define the data structures and basic
operations for designing, accessing,
maintaining, controlling, and protecting SQL
database
– Provide a vehicle for portability of database
definition and application modules between
conforming DBMSs
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SQL Standards: Key Benefits
Reduced training costs
Increased productivity
Improved application portability
Reduced dependence on a single vendor
Enhanced cross-system communications
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SQL: Components
Data Definition Language (DDL)
Three types of SQL commands
- Creating a database
– Commands that define a database, including
creating, altering, and dropping tables and
establishing constraints
Maintain and
Data Manipulation Language (DML) -query
the
– Commands that maintain and query a
database
Data Control Language (DCL)
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– Commands that control a database,
including administering privileges and
committing data
database
SQL: Data Definition Language
 Data Definition Language (DDL) consists of the
SQL commands used to define a database,
including
– Creating, altering, dropping tables and established
constraints
 For production (operational) databases, DDL
commends usually are restricted to DBA to
protect a fundamental database structure from
unexpected or accidental changes
it's like giving the keys to the castle only to those who are trained
and responsible for it, to prevent accidents or mistakes that could
disrupt the database's operation
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DDL Commands
 Table-related commands: Defines a table and its columns
– CREATE TABLE
– DROP TABLE
– ALTER TABLE - Make changes to an existing database
 Index-related commands: Defines an index on one column
or a concatenation of columns that enables rapid access to
the rows of a table Makes it easier and faster
– CREATE INDEX
– DROP INDEX
 View-related commands: Defines a logical table from one or
Virtual table
more tables or views
– CRETAE VIEW
– DROP VIEW
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Creating A Table: Process
 Select appropriate data type for each attribute,
including length, precision, and value range
 Determine the NULL value issue for each
attribute
 Determine the UNIQUE issue for each attribute
 Determine the primary key and foreign key(s)
 Determine the DEFAULT value issue for each
attribute
 Determine the update and delete behavior
 Create the table
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Create Table: Data Dictionary
Shows the columns in the EMPLOYEE table
Attribute
SSN
Char
9
First
Varchar
15
NN
Last
Varchar
15
NN
Birth_Date Date
--
Address
Varchar
20
Gender
Char
1
Salary
Decimal
Dep_No
Char
DEPARTMENT
EMPLOYEE
10
Data type Length Unique Null PK
Y
Dep_No Char(3),
FOREIGN KEY (Dep_No)
REFERENCES Department(Dept_No)
10.2
3
DEPARTMENT (Dept_No)
Dept_Name Dept_No Location
SSN First Last BirthDate
FK
PK - Primary key
NN- not null, cannot be a null value
FK - Foreign key
Y - It is the primary key
Address Gender Salary Dept_No
Create Table: Data Dictionary (2)
DEPARTMENT TABLE
Attribute
Data type Length Unique Null PK
Dept_Name
Varchar
15
Dept_No
Char
3
Location
Varchar
50
FK
Y
Y
NN
-DEPARTMENT NAME IS UNIQUE - TWO HUMAN --RESOURCES IN
COMPANY
LOCATION CANNOT BE NULL
NO FOREIGN KEY FOR DEPARTMENT TABLE
* Foreign key and Primary
key should have the same
Dept_Name Dept_No Location
DEPARTMENT
data type
EMPLOYEE
SSN First Last BirthDate
Address Gender Salary Dept_No
CREATE DATA DICTIONARY BASED ON THE LOGICAL SCHEMA
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Creating A Table: Data Type (1)
 Varchar(M) Variable character
– Variable Character Field is a set of character data of indeterminate length
– M represents the maximum column length in characters
 Char (M) Characters
– Character Field is a set of character data of determinate length
– M represents the column length in characters
 Text
– Extremely long field for text. May not be used as key and can be difficult
to sort
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Creating A Table: Data Type (2)
 Integer
Fixed length
– Ranging from -2,147,483,648 to 2147,483,647.
 Decimal (M,D)
– M is the total number of digits and D is the number
of digits after the decimal point.
– The maximum number of digits (M) is 65
 Date
– Ranging from '1000-01-01' to '9999-12-31' in
'YYYY-MM-DD' format
 TIME
– Ranging from '-838:59:59' to '838:59:59' in
'HH:MM:SS' format
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Table Creation: Syntax
Simplified syntax for CREATE TABLE:
define table name
CREATE TABLE tablename
({column definition [constraint]}, …);
define 1st column
define 2nd column
where format of column definition:
column_name
{datatype [(size)]}
format of constraint:
[CONSTRAINT constraint_name]
Constraint_type [constraint_attributes]
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Create Table: Example
table name
CREATE TABLE PROJECT(
1st columnchar with length of '3'
Prj_No char(3) primary key,
2nd column
Prj_Name varchar(30) not null UNIQUE,
3rd column
Dep_No char(3),
CONSTRAINT FK_PRJ_DEPT foreign key
(Dep_No) references DEPT(D_No) on delete
SET NULL
);
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Order Management Database Example
Customer_ID
CUSTOMER
1..1
Name
City
TEL
State
O_No
Order_Date
Ship_Date
Shipping_Addr
Status
Payment
Contact
1..1
TEL
Status
MSPR
Name
Provides
Product_ID
Cost
0..N
PRODUCT_
Consists_Of
ORDER 0..N
1..M
Order_Cycle
0..N
PRODUCT
1..1
Keeps
0..N
INVENTORY
1..1
Quantity
Is_Created
_For
0..N
PROMOTION
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Name
VENDOR
ZIP
Address
Places
VID
Street
PM_No
Effective_Date
End_Date
Sales_Price
Quantity
Stack_No
Order Management Database Example
VENDOR
VID
PRODUCT
Product_ID
VName
Contact TEL Order_Cycle
Product_Name
VID
Status MSRP Cost
INVENTORY
Stack_No Product_ID Quantity
PROMOTION
PM_No
ORDER_DETAIL
O_No
PORDER
O_No
CUSTOMER
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Product_ID Sales_Price Eff_Date End_Date
Product_ID Quantity
Order_Date Customer_ID Ship_Date
Customer_ID
Customer_Name
Ship_Addr
TEL Street
Status Payment
City State ZIP
Create Table: Example (1)
CREATE TABLE VENDOR(
VID char (10),
Comma(,) to separate attributes
VName varchar(50) NOT NULL UNIQUE,
Contact varchar(50),
TEL char(10),
Semi-colon(;) to end a command
Order_Cycle char(25),
CONSTRAINT PK_Vendor primary key (VID));
keyword
primary key for the vendor
Defining multiple columns together as the primary key
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Create Table: Example (1)
CREATE TABLE VENDOR(
VID char (10),
VName varchar(50) NOT NULL UNIQUE,
Contact varchar(50),
TEL char(10),
Details of the constraint
Order_Cycle char(25),
CONSTRAINT PK_Vendor primary key (VID));
Keyword for defining a constraint
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Name of the constraint
Create Table: Example (2)
CREATE TABLE VENDOR(
VID char (10) PRIMARY KEY,
VName varchar(50) NOT NULL UNIQUE,
Contact varchar(50),
TEL char(10),
Order_Cycle char(25));
Define the primary key as an anonymous constraint.
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Named versus Anonymous Constraints
When a constraint is created without a
name, the DBMS will assign one (such as
PK__B__B_COL1__75435199)
Benefits of naming a constraint
– If a query (insert, update, delete) violates a
constraint, SQL will generate an error message
that will contain the constraint name. If the
constraint name is clear and descriptive, the
error message will be easier to understand
– If a constraint needs to be modified in the
future, it's very hard to do if you don't know what
it's named
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Exercise
Please create the table CUSTOMER
based on the following specification
Attribute
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Data type Length Unique Null PK
Customer_ID
char
10
Y
Customer_Name
varchar
50
NN
TEL
char
10
NN
Address
varchar
100
City
varchar
30
State
char
2
ZIP
char
5
FK
Solution
CREATE TABLE CUSTOMER(
Customer_ID char(10) primary key,
Customer_name varchar(50) Not null,
tel char(10) not null,
address varchar(100),
city varchar(30),
state char(2),
zip char(5)
);
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SQL Constraints
 SQL constraints are used to specify rules for
data in a table
– NOT NULL - Ensures that a column cannot have a
NULL value
– UNIQUE - Ensures that all values in a column are
different
– PRIMARY KEY - A combination of a NOT NULL and
UNIQUE. Uniquely identifies each row in a table
– FOREIGN KEY - Uniquely identifies a row/record in
another table
– DEFAULT - Sets a default value for a column when
no value is specified
– INDEX - Used to create and retrieve data from the
database very quickly
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Create Table with FK: Example (1)
Create Table PRODUCT (
Product_ID char(13) primary key,
Product_Name varchar(50) not null unique,
to define
VID char(10) references Vendor(VID), Used
foreign key
Status char(10),
MSRP decimal(10.2),
Cost decimal (10.2) not null
);
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Create Table with FK: Example (2)
Create Table INVENTORY (
Stack_No char(10),
Product_ID char(13) references Product(Product_ID),
Quantity integer,
Constraint PK_Inventory primary key (Stack_NO)
);
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Exercise
Please create the table PORDER based
on the following specification
Attribute
Data type Length Unique Null PK
O_No
char
Order_Date
date
Customer_ID char
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10
FK
Y
NN
10
Ship_Date
date
Ship_Addr
varchar
300
Status
varchar
50
Payment
varchar
50
NN
Customer(Customer_ID)
Solution 1
CREATE TABLE PORDER (
O_No char(10),
Order_Date date not null,
Customer_ID char(10) not null,
Ship_Date date,
Ship_Addr varchar(300),
Status varchar(50),
Payment varchar(50),
CONSTRAINT PK_PORDER primary key(O_No),
CONSTRAINT FK_PORDER_CUST foreign key
(Customer_ID) references Customer(Customer_ID)
);
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Solution 2
CREATE TABLE PORDER (
O_No char(10) primary key,
Order_Date date not null,
Customer_ID char(10) not null references
Customer(Customer_ID),
Ship_Date date,
Ship_Addr varchar(300),
Status varchar(50),
Payment varchar(50)
);
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Create Table with FK: Example (3)
Create Table ORDER_DETAIL (
O_No char(10),
Product_ID char(13) not null,
Quantity integer,
Constraint PK_ODetail primary key (O_No, Product_ID),
Constraint FK_OD_PO foreign key (O_No) references
PORDER(O_No),
Constraint FK_OD_PRD foreign key (Product_ID) references
Product(Product_ID)
);
Defines the composite primary key!
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Default Value
The DEFAULT constraint is used to insert
a default value into a column when that
column is left blank.
Create Table Promotion (
PM_No char(10) primary key,
Product_ID char(13) not null references Product(Product_ID) ,
Sales_Price decimal(10,2) DEFAULT 9.99,
Eff_Date date not null,
End_Date date
);
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Removing Tables
Use DROP TABLE statement to remove
a table and all its data
– CREATE commands may be reversed by
using a DROP command.
– DROP TABLE destroys a table, including its
definition, contents, and any constraints
associated with it.
Example
name of the table
– DROP TABLE ORDER_DETAIL;
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Changing Table Definitions (1)
ALTER TABLE statement may include
keywords
ADD: add new columns to an existing
table
Add a gender column to CUSTOMER table
ALTER TABLE CUSTOMER
ADD (gender VARCHAR(1)); Add column
– When a new column is added, its value will
be NULL for all existing rows.
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Changing Table Definitions (2)
MODIFY: Change the columns’ names,
datatype, lengths, and constraints
– Change the length of Ship_Addr to 500
ALTER TABLE PORDER
Modify ship_Addr varchar(500);
DROP: Remove one columns from a table
– Drop the attribute Order_Cycle from the Vendor
TABLE
ALTER TABLE VENDOR
DROP Order_Cycle;
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Exercise
Please use the ALTER TABLE command
to modify the VENDOR table on the
Contact column to make the length as 30
Please use the ALTER TABLE command
to modify the VENDOR table to set TEL
as unique
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Solution
ALTER TABLE VENDOR
MODIFY contact varchar(30);
ALTER TABLE VENDOR
MODIFY tel char(10) unique;
≡
ALTER TABLE VENDORMODIFY contact
varchar(30),MODIFY tel char(10) unique;
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Changing Table Definitions (3):
Rename Table
We can use the following statements to
rename a table:
ALTER TABLE <table_name>
RENAME TO <new_table_name>;
For example, we can change the table
name “vender” to “supplier”
ALTER TABLE VENDOR
RENAME TO SUPPLIER;
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