Contents
How do you make a foreign key a primary key in SQL?
2 Answers. A column can be both a primary key and a foreign key. For example: create table t1 ( id int not null , constraint PK_T1 primary key (id) ); create table t2 ( id int not null , constraint PK_T2 primary key (id) , constraint FK_T2_ID foreign key (id) references t1(id) );
How do we represent primary key and foreign key?
Foreign key is a field in the table that is primary key in another table. Primary Key can’t accept null values. Foreign key can accept multiple null value. By default, Primary key is clustered index and data in the database table is physically organized in the sequence of clustered index.
How is a foreign key related to a primary key?
A foreign key is a field or collection of fields in a table that refers to the Primary key of the other table. It is responsible for managing the relationship between the tables. The table which contains the foreign key is often called the child table, and the table whose primary key is being referred by the foreign key is called the Parent Table.
Do you need a foreign key for a parent table?
For defining a Foreign key, we need a parent table with a Primary Key. Primary key creates clustered indexes on the table. Foreign key does not create indexes on the table neither clustered nor unclustered. In this tutorial, we have seen what a Primary and a Foreign Key is.
Can a foreign key contain a duplicate value?
A foreign key can contain duplicate values. There is no limitation in inserting the values into the table column. While inserting any value in the foreign key table, ensure that the value is present into a column of a primary key.
When to use FOREIGN KEY constraint in SQL?
SQL foreign key constraint is used to make sure the referential integrity of the data parent to match values in the child table. Below is the syntax of Primary Key: CREATE TABLE ( Column1 datatype, Column2 datatype, PRIMARY KEY (Column-Name) .