How to reference a foreign key in PostgreSQL?

How to reference a foreign key in PostgreSQL?

In this syntax:

1. First, specify the name for the foreign key constraint after the CONSTRAINT keyword.
2. Second, specify one or more foreign key columns in parentheses after the FOREIGN KEY keywords.
3. Third, specify the parent table and parent key columns referenced by the foreign key columns in the REFERENCES clause.

What is primary key and foreign key in PostgreSQL?

The PostgreSQL FOREIGN KEY is a combination of columns with values based on the primary key values from another table. A foreign key constraint, also known as Referential integrity Constraint, specifies that the values of the foreign key correspond to actual values of the primary key in the other table.

How to inherit a table in PostgreSQL?

Table inheritance is typically established when the child table is created, using the INHERITS clause of the CREATE TABLE statement. Alternatively, a table which is already defined in a compatible way can have a new parent relationship added, using the INHERIT variant of ALTER TABLE.

Which table should contain foreign key?

child table
The table that contains the foreign key is considered the child table, and the table that the foreign key references is the parent table. The foreign key restricts what data can be stored in the foreign key columns in the child table, based on the data in the referenced columns in the parent table.

Why do I have foreign keys in PostgreSQL?

In the parent-child relationship, the parent table keep the initial column values, and the child table’s column values reference the parent column values. Note: A PostgreSQL table can have various foreign keys depending on its connection with other tables.

Can a foreign key be a primary key?

In such a scenario, the child full-photo table carries the ID of its parent thumbnail row as a foreign key. That foreign key column could logically serve as the primary key as well. Can I designate that one column of a child to be both a foreign key and also a primary key?

How to add a foreign key to a table?

The below illustrations of the ALTER TABLE statement to add a foreign key in the existing table: 1 ALTER TABLE child_table 2 ADD CONSTRAINT [constraint_name] 3 FOREIGN KEY (fk_columns) 4 REFERENCES parent_table (parent_key_columns);

When to set null to the foreign key?

The SET NULL automatically sets NULL to the foreign key columns in the referencing rows of the child table when the referenced rows in the parent table are deleted. The following statements drop the sample tables and re-create them with the foreign key that uses the SET NULL action in the ON DELETE clause: