No Clocks

The following illustrates a foreign key constraint syntax: [CONSTRAINT fk_name] FOREIGN KEY(fk_columns) REFERENCES parent_table(parent_key_columns) [ON DELETE delete_action] [ON UPDATE update_action]

In this syntax: First, specify the name for the foreign key constraint after the CONSTRAINT keyword. The CONSTRAINT clause is optional. If you omit it, PostgreSQL will assign an auto-generated name. Second, specify one or more foreign key columns in parentheses after the FOREIGN KEY keywords. Third, specify the parent table and parent key columns referenced by the foreign key columns in the REFERENCES clause. Finally, specify the desired delete and update actions in the ON DELETE and ON UPDATE clauses.

Since the primary key is rarely updated, the ON UPDATE action is infrequently used in practice. We’ll focus on the ON DELETE action.

PostgreSQL supports the following actions: SET NULL SET DEFAULT RESTRICT NO ACTION CASCADE

To copy a table completely, including both table structure and data, you use the following statement: CREATE TABLE new_table AS TABLE existing_table;

When to use temporary tables Isolation of data: Since the temporary tables are session-specific, different sessions or transactions can use the same table name for temporary tables without causing a conflict. This allows you to isolate data for a specific task or session. Intermediate storage: Temporary tables can be useful for storing the intermediate results of a complex query. For example, you can break down a complex query into multiple simple ones and use temporary tables as the intermediate storage for storing the partial results. Transaction scope: Temporary tables can be also useful if you want to store intermediate results within a transaction. In this case, the temporary tables will be visible only to that transaction