postgresql add foreign key to existing table

Postgresql add foreign key to existing table update#

We will not go beyond this simple example in this tutorial, but just refer you to Chapter 5 for more information. The behavior of foreign keys can be finely tuned to your application.

Postgresql add foreign key to existing table update#

INSERT INTO weather VALUES ('Berkeley', 45, 53, 0.0, '') ĮRROR: insert or update on table 'weather' violates foreign key constraint 'weather_city_fkey'ĭETAIL: Key (city)=(Berkeley) is not present in table 'cities'. The new declaration of the tables would look like this:Ĭity varchar(80) references cities(name), This approach has a number of problems and is very inconvenient, so PostgreSQL can do this for you. In simplistic database systems this would be implemented (if at all) by first looking at the cities table to check if a matching record exists, and then inserting or rejecting the new weather records. This is called maintaining the referential integrity of your data. The execution to perform the task is done in a command. First step, connect to the PostgreSQL Database. The following are steps to execute in the form of several activities. In order to perform it, there are a few step create the necessary table to simulate it. Once MySQL finishes importing data, go ahead and run an ALTER TABLE query to add a foreign key: this might seem a little counterintuitive since we just told. Consider the following problem: You want to make sure that no one can insert rows in the weather table that do not have a matching entry in the cities table. The task is to add a foreign key constraint in a certain table. Recall the weather and cities tables from Chapter 2.