How do I create a foreign key in MySQL workbench?
To add a foreign key, click the last row in the Foreign Key Name list. Enter a name for the foreign key and select the column or columns that you wish to index by checking the column name in the Column list….Figure 8.16 The Foreign Keys Tab
- RESTRICT.
- CASCADE.
- SET NULL.
- NO ACTION.
What is foreign key in MySQL workbench?
The foreign key is used to link one or more than one table together. It is also known as the referencing key. A foreign key matches the primary key field of another table. It means a foreign key field in one table refers to the primary key field of the other table.
How do I add a foreign key to a table in MySQL?
Here’s the syntax to create foreign key in MySQL. ALTER TABLE table_name ADD CONSTRAINT constraint_name FOREIGN KEY (foreign_key_name,…) REFERENCES parent_table(column_name,…); In the above query, table_name is the the table where you want to add foreign key.
What is foreign key in MySQL?
A foreign key is a column or group of columns in a table that links to a column or group of columns in another table. The foreign key places constraints on data in the related tables, which allows MySQL to maintain referential integrity.
Does a foreign key have to be a primary key?
Primary keys always need to be unique, foreign keys need to allow non-unique values if the table is a one-to-many relationship. It is perfectly fine to use a foreign key as the primary key if the table is connected by a one-to-one relationship, not a one-to-many relationship.
What is difference between primary key and foreign key?
A primary key is used to ensure data in the specific column is unique. A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. It uniquely identifies a record in the relational database table. Only one primary key is allowed in a table.
What is the difference between primary key and unique key?
A primary key is a column of table which uniquely identifies each tuple (row) in that table. Unique key constraints also identifies an individual tuple uniquely in a relation or table. A table can have more than one unique key unlike primary key.
Can foreign key be a primary key?
Yes, it is legal to have a primary key being a foreign key. This is a rare construct, but it applies for: a 1:1 relation. The two tables cannot be merged in one because of different permissions and privileges only apply at table level (as of 2017, such a database would be odd).
Can Unique Key be a primary key?
A primary key must be unique. A unique key does not have to be the primary key – see candidate key. That is, there may be more than one combination of columns on a table that can uniquely identify a row – only one of these can be selected as the primary key.
Can we use unique key as a primary key?
Primary Key is a column that is used to uniquely identify each tuple of the table. It is used to add integrity constraints to the table. Only one primary key is allowed to be used in a table….Difference between Primary Key and Unique Key.
| Primary Key | Unique Key |
|---|---|
| present in a table | present in a table |
Can 2 tables have same primary key?
Yes. You can have same column name as primary key in multiple tables. Column names should be unique within a table. A table can have only one primary key, as it defines the Entity integrity.