Frequent question: How can delete foreign key constraint in SQL Server using query?

How do I delete a foreign key constraint in SQL Server?

To delete a foreign key constraint

1. In Object Explorer, expand the table with the constraint and then expand Keys.
2. Right-click the constraint and then click Delete.
3. In the Delete Object dialog box, click OK.

Can we delete foreign key data?

A foreign key with cascade delete means that if a record in the parent table is deleted, then the corresponding records in the child table will automatically be deleted. … A foreign key with cascade delete can be created using either a CREATE TABLE statement or an ALTER TABLE statement.

How do I remove a foreign key from an existing table?

You can drop a foreign key constraint using the following ALTER TABLE syntax: ALTER TABLE tbl_name DROP FOREIGN KEY fk_symbol; If the FOREIGN KEY clause defined a CONSTRAINT name when you created the constraint, you can refer to that name to drop the foreign key constraint.

How can I delete primary key and foreign key in SQL?

Using SQL Server Management Studio

1. In Object Explorer, expand the table that contains the primary key and then expand Keys.
2. Right-click the key and select Delete.
3. In the Delete Object dialog box, verify the correct key is specified and click OK.

Where is foreign key constraint in SQL Server?

Using SQL Server Management Studio

1. Open the Table Designer for the table containing the foreign key you want to view, right-click in the Table Designer, and choose Relationships from the shortcut menu.
2. In the Foreign Key Relationships dialog box, select the relationship with properties you want to view.

What is foreign key and example?

A foreign key is a set of attributes in a table that refers to the primary key of another table. … For example, a table called TEAM may have an attribute, MEMBER_NAME, which is a foreign key referencing a candidate key, PERSON_NAME, in the PERSON table.

Can we delete primary key without deleting foreign key?

If you want the department to remain and to be able to do this, you will need to alter the foreign key to include ON DELETE SET NULL. Otherwise, you will have to drop the constraint, perform the delete, and recreate the constraint.

What happens if we delete foreign key?

When a referenced foreign key is deleted or updated, respectively, the columns of all rows referencing that key will be set to NULL . The column must allow NULL or this update will fail.

Can we delete primary key before foreign key?

If an attempt is made to delete the row in a primary key table or to change a primary key value, the action will fail when the deleted or changed primary key value corresponds to a value in the foreign key constraint of another table.

Which clause is used to remove a foreign key constraint?

To remove a foreign key constraint, the ‘DROP’ clause is used.

Is foreign key can be NULL?

Short answer: Yes, it can be NULL or duplicate. I want to explain why a foreign key might need to be null or might need to be unique or not unique. First remember a Foreign key simply requires that the value in that field must exist first in a different table (the parent table).

Can we drop primary key constraint?

To drop primary key constraints, use the DROP PRIMARY KEY clause of the ALTER TABLE statement. … Alternatively, you can use the ALTER TABLE statement with the DROP CONSTRAINT option. To drop foreign key (referential) constraints, use the DROP CONSTRAINT clause of the ALTER TABLE statement.

What is the rule of primary key in database?

Rules for Primary Key

All the values in the column chosen as the primary key must be unique. Each and every table can have only one primary key. No value in the primary key column can be NULL. You cannot insert a new row with a pre-existing primary key.