postgresqlHow do I create a foreign key in PostgreSQL?

Creating a foreign key in PostgreSQL is a simple process. First, create a table with the necessary columns and data types. For example:

CREATE TABLE parent_table (
   id SERIAL PRIMARY KEY,
   name VARCHAR(50) NOT NULL
);

Then, create a second table with a foreign key column that references the primary key from the first table.

CREATE TABLE child_table (
   id SERIAL PRIMARY KEY,
   parent_id INTEGER REFERENCES parent_table(id)
);

The REFERENCES clause in the above statement creates a foreign key constraint. This constraint ensures that the value of the parent_id column in the child_table must match the value of the id column in the parent_table.

You can also add additional constraints, such as ON DELETE CASCADE, to the foreign key. This will ensure that when a row in the parent table is deleted, all corresponding rows in the child table are also deleted.

CREATE TABLE child_table (
   id SERIAL PRIMARY KEY,
   parent_id INTEGER REFERENCES parent_table(id) ON DELETE CASCADE
);

For more information on creating foreign key constraints in PostgreSQL, see the official documentation: https://www.postgresql.org/docs/current/ddl-constraints.html#DDL-CONSTRAINTS-FK

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