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What is a FOREIGN KEY constraint in PostgreSQL?
A foreign key constraint specifies that the values in a column (or a group of columns) must match the values appearing in some row of another table. We say this maintains the referential integrity between two related tables. Say you have the product table that we have used several times already:
What does a constraint do in PostgreSQL SQL?
To that end, SQL allows you to define constraints on columns and tables. Constraints give you as much control over the data in your tables as you wish. If a user attempts to store data in a column that would violate a constraint, an error is raised. This applies even if the value came from the default value definition. 5.3.1.
Can a column constraint be written as a table constraint?
Column constraints can also be written as table constraints, while the reverse is not necessarily possible, since a column constraint is supposed to refer to only the column it is attached to. ( PostgreSQL doesn’t enforce that rule, but you should follow it if you want your table definitions to work with other database systems.)
How to limit PostgreSQL 9.2 tstzrange null / infinity?
I’d like to limit a PostgreSQL 9.2 tstzrange to valid dates at both ends. No NULLs nor ‘infinity’. Various revisions of this SQL isn’t constraining ‘-/+infinity’ input:
How to create a foreign table in PostgreSQL?
Sort operation is performed on local postgres server, not on remote. If your code always sort the results, you can just create a view on remote postgres with order by clause and then create a foreign table pointing to the view. Thanks for contributing an answer to Database Administrators Stack Exchange!
How do you specify a constraint in PostgreSQL?
So, to specify a named constraint, use the key word CONSTRAINT followed by an identifier followed by the constraint definition. (If you don’t specify a constraint name in this way, the system chooses a name for you.) A check constraint can also refer to several 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: