![]() ![]() Let's look at an example of how to create a foreign key in SQL Server (Transact-SQL) using the ALTER TABLE statement. The foreign key will enforce a link between this data and the child_col1, child_col2. parent_col3 The columns that make up the primary key in the parent_table. parent_table The name of the parent table whose primary key will be used in the child_table. child_col_n The columns in child_table that will reference a primary key in the parent_table. fk_name The name of the foreign key constraint that you wish to create. parent_col_n) child_table The name of the child table that you wish to modify. REFERENCES parent_table (parent_col1, parent_col2. The syntax for creating a foreign key using an ALTER TABLE statement in SQL Server (Transact-SQL) is: ALTER TABLE child_table So in this example, our foreign key called fk_inv_product references the products table based on two fields - the product_name and location fields.Ĭreate a foreign key - Using ALTER TABLE statement Syntax Therefore, our child table and foreign key must also reference these two columns. In this foreign key example, our parent table called products has a primary key that consists of both the product_name and location columns. REFERENCES products (product_name, location) Let's look at how to create a foreign key with one than one field.ĬONSTRAINT products_pk PRIMARY KEY (product_name, location) This first example shows how to create a foreign key involving one column. The foreign key establishes a relationship between the product_id column in the inventory table and the product_id column in the products table. We have used the CREATE TABLE statement to create a foreign key on the inventory table called fk_inv_product_id. Next, we've created a second table called inventory that will be the child table in this foreign key example. The products table has a primary key that consists of the product_id field. In this foreign key example, we've created our parent table as the products table. Let's look at an example of how to create a foreign key in SQL Server (Transact-SQL) using the CREATE TABLE statement. It means that the child data is set to their default values when the parent data is deleted or updated. SET DEFAULT It is used in conjunction with ON DELETE or ON UPDATE. It means that the child data is set to NULL when the parent data is deleted or updated. SET NULL It is used in conjunction with ON DELETE or ON UPDATE. It means that the child data is either deleted or updated when the parent data is deleted or updated. ![]() CASCADE It is used in conjunction with ON DELETE or ON UPDATE. It means that no action is performed with the child data when the parent data is deleted or updated. NO ACTION It is used in conjunction with ON DELETE or ON UPDATE. You have the options of NO ACTION, CASCADE, SET NULL, or SET DEFAULT. It specifies what to do with the child data when the parent data is updated. ![]() It specifies what to do with the child data when the parent data is deleted. ![]() The column should either be defined as NULL or NOT NULL and if this value is left blank, the database assumes NULL as the default. column1, column2 The columns that you wish to create in the table. ) child_table The name of the child table that you wish to create. The syntax for creating a foreign key using a CREATE TABLE statement in SQL Server (Transact-SQL) is: CREATE TABLE child_tableįOREIGN KEY (child_col1, child_col2. Create Foreign key - Using CREATE TABLE statement Syntax ![]()
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