Here, the book_id field is a foreign key for this table and every value of this field must exist in the id field of books table. Make a connection with MySQL server using the mysql client and run the following SQL statements to create the database and the tables.ĭefine Foreign Key Constraint using CREATE statementĬreate a table named ‘ book_borrow_info‘ with foreign key constraints by executing the following statement. Suppose the database name is ‘ library’ and it contains two parent tables named ‘ books’ and ‘ borrower’. One by using the CREATE statement and another by using the ALTER statement.īefore creating a foreign key constraint, you have to create a database and parent table with the primary key. A foreign key can be created in two ways.
#Mysql foreign key update#
References privileges or at least one of the privileges of the SELECT, INSERT, UPDATE and DELETE statements is required to create a foreign key.Any index column or multiple columns can be referenced as a foreign key for the InnoDB table only.
Some important features of foreign key constrain are explained below. The features of foreign keys and how these keys can be used in MySQL tables are shown in this article. The primary key is a unique key for a table to identify the particular row in the table and when this primary key is used into another table to make one-to-one or one-to-many or many-to-many relationship then it is called a foreign key. To define any foreign key constraint for any table you have to use the primary key of another table. It is a very important feature of MySQL to set different types of restrictions on the related tables. The foreign key constraint is used to make a relationship between two tables in the MySQL database.
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