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SQL ConstraintMade By:
Israa Al- JarrahCIS Dept-- IT Faculty
OUT LINE
SQL Constraint Meaning SQL Constraint Meaning
Constraint Type Constraint Type
Write Constraint Write Constraint
Constraint
Meaning :-
Constraints can be specified when a table is created (with the
CREATE TABLE statement) or after the table is created (with the ALTER TABLE statement)Constraints are used to limit
the type of data that can go into a table.
Constraint Write:-
Constraint
[Constraint name]
Constraint Type
Constraint Implementation
Way :--
You can define constraints syntactically in two ways:1. As part of the definition of an individual column or attribute. This
is called inline specification.
2. As part of the table definition. This is called out-of-
line specification.
Constraint Type:-
Types of constraints: 1.Integrity constraints 2.Value constraintsTable constraint
Restricts data value with respect to all other values in table
1 .Not Null
2 .Unique Key
3 .Primary Key
4 .Foreign Key
5 .Check Key
6 .Default Key
Constraint Type:-
Constraint Type:-
Not Null
constraint enforces a column to NOT accept NULL values. constraint
enforces a column to NOT accept NULL values. This means that you cannot
insert a new record, or update a record without adding a value to
this field.Expression of Not Null we use short cut NN
Constraint Type:-
1 .Not Null Example-:
Create Table Language( Language_Name varchar2(30), Language_Id number(15) Constraint Constraint_Language_language_name_NN Not Null);
Constraint Implementation
Way :-- NOT NULL Constraints
& Default Constraint Must be declared inline.
Constraint Implementation
Way :--
All other constraints can be declared either inline or out of line.
Constraint Type:-
2 .Unique Key
The UNIQUE constraint uniquely identifies each
record in a database table.
Constraint Type:-
Example 2. Unique Key
Create Table Person( Person_Id number(15) Constraint Person_person_id_UN Unique Person_name varchar2(40), Person_BD Date);
Constraint Type:-
Example 2. Unique Key
Create Table Person( Person_Id number(15), Person_name varchar2(40), Person_BD Date
Constraint Person_person_id_UN Unique
(Person_Id));
Constraint Type:-
3 .Primary Key
Primary keys must contain unique values
A primary key column cannot contain NULL values.
Each table should have a primary key, and each table can
have only ONE primary key
Constraint Type:-
3 .Primary Key Example
CREATE TABLE locations_demo) location_id NUMBER(4) Constraint Constraint_loc_id_pk PRIMARY KEY , street_address VARCHAR2(40) , postal_code VARCHAR2(12) );
Constraint Type:-
3 .Primary Key Example
CREATE TABLE locations_demo) location_id NUMBER(4) , street_address VARCHAR2(40) , postal_code VARCHAR2(12) , Constraint Constraint_loc_id_pk PRIMARY KEY (Location_id));
Constraint Type:-
Unique Key Unique Key
Primary Key
Constraint Type:-
Unique Key Unique Key accept only one null value
unique key use many time in table.
Constraint Type:-
Unique Key Primary KeyPrimary key does not accept
null value primary key use only
one time in table.
Constraint Type:-
Unique Key4 .Foreign Key
A FOREIGN KEY in one table points to a PRIMARY KEY in another table
The FOREIGN KEY constraint is used to prevent actions that would destroy links between
tables.
Constraint Type:-
Unique Key
4 .Foreign Key Example
CIty Address FirstName LastName P-Id
Sandnes Timoteivn10
Ola Hansen 1
Sandnes Borgvn23 Tove Svendson 2
Sandnes Storagt 20 Kari Pettersen 3
The "Persons" table:
Constraint Type:-
Unique Key
4 .Foreign Key Example
P_id OrderNo O_Id
3 77895 1
3 44678 2
2 22456 3
1 24562 4
The “Order" table:
Constraint Type:-
4 .Foreign Key Example
Note"P_Id" column in the "Orders"
table points to the "P_Id" column in the "Persons" table.
The "P_Id" column in the "Persons" table is the PRIMARY KEY in the
"Persons" table.The "P_Id" column in the "Orders"
table is a FOREIGN KEY in the "Orders" table.
Constraint Type:-
4 .Foreign Key Example
First step must create “Person” Table
Create Table Person ( P_Id number Constraint constraint_person_person_Id_PK primary key, LastName varcahr2(45), FirstName varchar2(45), Address varchar2(45), City varchar2(45));
Constraint Type:-
4 .Foreign Key Example
Create Table Order (Order_id number(15) CONSTRAINT con_Order_id_pk Primary Key,OredrNO number(30) ,P_id number(15) CONSTRINT con_person_order_id_FK refernace Person (p_id));
Constraint Type:-
5 .Check Key
The CHECK constraint is used to limit the value range that can be
placed in a column. If you define a CHECK constraint
on a single column it allows only certain values for this column
Constraint Type:-
5 .Check Key Example
CREATE TABLE divisions (div_no NUMBER CONSTRAINT check_divno CHECK (div_no BETWEEN 10 AND 99),
div_name VARCHAR2(9) CONSTRAINT check_divname_cc CHECK (div_name = UPPER(div_name))
);
Constraint Type:-
5 .Check Key 6 .Default Key
The DEFAULT constraint is used to insert a default value into a
column The default value will be added to all new records
if no other value is specified.
Constraint Type:-
5 .Check Key 6 .Default Key Example
CREATE TABLE Persons( P_Id Number(15), LastName varchar(255), FirstName varchar(255), Address varchar(255), City varchar(255) DEFAULT 'Sandnes');
Composite Key
CONSTRAINT constraint_name PRIMARY KEY (columnname1, columnname2 …)
Composite Key
Example
Create table person(
Person_ID Number(15),Person_phone number(15),Constraint con_person_un
Unique(Person_ID,Person_Phone)
);
Reference http://www.w3schools.com/sql/sql_constraints.asp
http://www.docs.oracle.com/cd/B19306_01/server.102/b14200/clauses002.htm#i1015609
Thank you for listen
Israa jarrah