How do I reference a foreign key in PostgreSQL?

Posted on by Dominique Stacey

How do I 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.

How do I add a foreign key to a table in PostgreSQL?

You can create a foreign key directly from the GUI Tool.

  1. Select to view table orders from the right sidebar.
  2. Switch to structure tab at the bottom bar.
  3. Choose customer_id column and add a foreign key in the foreign_key field.

How do you DESC a table in PostgreSQL?

Use the ‘d’ command in psql to describe a Postgres table. We can use the \d or \d+ commands, followed by the table name, to query and retrieve information on the columns of a table.

What is the use of foreign key in PostgreSQL?

PostgreSQL foreign key constraint specifies the values in a group of columns or a column in the Child table, equivalent to the values in a group of columns or a column of the Parent table. In other words, we can say that a foreign key makes it possible to generate a parent-child relationship with the tables.

Can a foreign key be a primary key PostgreSQL?

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.

How do I list all tables in PostgreSQL?

Use the \dt or \dt+ command in psql to show tables in a specific database. Use the SELECT statement to query table information from the pg_catalog. pg_tables catalog.

How do you describe a table in PostgreSQL pgAdmin?

In pgAdmin 4, we are going to use the information_schema for describing the tables….PostgreSQL DESCRIBE TABLE using pgAdmin 4

  1. SELECT COLUMN_NAME.
  2. FROM information_schema. COLUMNS.
  3. WHERE TABLE_NAME = ‘customer’;

Can foreign key be primary key of same table?

If you mean “can foreign key ‘refer’ to a primary key in the same table?”, the answer is a firm yes as some replied.

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).

Why is my foreign key NULL?

A: Whether or not a column can contain a NULL value is determined by the presence or absence of a NOT NULL constraint. This is entirely independent of whether the column is referenced in a foreign key constraint. The value in the column is NULL because that’s the value that was assigned when the row was inserted.