Skip to main content

FOREIGN KEY constraint in sql server

FOREIGN KEY- This constraints responsible to uniquely identified a rows or records to another table.

Example-

Following table structure can clear your concept of foreign key constraint.

Product Table

CREATE TABLE PRODUCT
(
ID INT NOT NULL IDENTITY(1,1),
SKU VARCHAR(20) NOT NULL,
TITLE VARCHAR(200) NOT NULL,
PRICE MONEY NOT NULL,
DISCRIPTION VARCHAR(2000)  NULL,
DTCREATE DATETIME NULL
CONSTRAINT pk_ID PRIMARY KEY (ID)
)

Product Order Table

CREATE TABLE PRODUCT_IMAGE
(
ID INT NOT NULL IDENTITY(1,1),
PRODUCT_ID INT NOT NULL REFERENCES PRODUCT(ID),
IMGURL VARCHAR(200) NOT NULL ,
DTCREATE DATETIME
)

To create foreign key constraint to existing table use following query.

ALTER TABLE PRODUCT_IMAGE ADD FOREIGN KEY (PRODUCT_ID) REFERENCES PRODUCT(ID)

Comments

Post a Comment

Popular posts from this blog

Constraints in sql server

Constraints   - Constraints are the rules enforced on data columns on table. This ensures the accuracy and reliability of the data in the database. Constraints define some conditions that restricts the column to remain true while inserting or updating or deleting data in column. Constraints can be defined in two ways   1) The constraints can be specified immediately after the column definition. This is called column-level definition.   2) The constraints can be specified after all the columns are defined. This is called table-level definition.   Types of Constraints in SQL-Server NOT NULL - This constraint is responsible for a column to confirm that a column cannot have a null value. DEFAULT – This constraint provides a default value when specified non for this column. UNIQUE - This constraint insure that each row for the column has different value. PRIMARY KEY - Primary key constraint is a combination of a NOT NULL constraint and a UNIQUE constra
Post a Comment
Read more

Bulk Update in sql server 2008..

/*Bulk update query*/ create table Table1 ( ID int identity ( 1 , 1 ), vIsbn varchar ( 20 ), dcPrice decimal ( 18 , 2 ) ) create table Table2 ( ID int identity ( 1 , 1 ), vIsbn varchar ( 20 ), dcPrice decimal ( 18 , 2 ) ) /*Here create two tables, we update Table1's dcPrice column from Table 2 Using Bulk update*/     insert into Table1 ( vIsbn , dcPrice ) values ( '9087657654312' , 0.00 ) insert into Table1 ( vIsbn , dcPrice ) values ( '9989876765454' , 0.00 ) insert into Table2 ( vIsbn , dcPrice ) values ( '9087657654312' , 10.20 ) insert into Table2 ( vIsbn , dcPrice ) values ( '9989876765454' , 20.10 ) select * from Table1 /*here bulk update Query*/ UPDATE Tbl SET dcPrice = Tbl2 . dcPrice FROM Table1 Tbl JOIN Table2 AS Tbl2 ON Tbl . vIsbn = Tbl2 . vIsbn select * from Table1 drop table Table1 dr
6 comments
Read more

DEFAULT constraint in sql server

DEFAULT – This constraint provides a default value when specified non for this column. Example- Following create a table PRODUCT, column DTCREATE has default value GETDATE() it will store system’s date-time by default if value is not specified for this column. CREATE TABLE PRODUCT ( ID INT NOT NULL, SKU VARCHAR ( 20 ) NOT NULL, TITLE VARCHAR ( 200 ) NOT NULL, PRICE MONEY NOT NULL, DISCRIPTION VARCHAR ( 2000 )   NULL, DTCREATE DATETIME DEFAULT GETDATE () ) If PRODUCT table has already been created and you want apply default price in PRICE column use following query (for SQL server). ALTER TABLE PRODUCT ADD CONSTRAINT DF_SomePrice DEFAULT 20.00 FOR PRICE
1 comment
Read more