Postgres and Open Source Experts

In PostgreSQL, the DISTINCT clause can be used with the COUNT() function to count only unique/distinct values of a table.

Foreign keys allows us to link the data of one table to others. The table referencing the foreign key is known as child table, while the table referenced by the foreign key is known as parent table.

In PostgreSQL, EXCEPT returns the rows that exist in the result set of the first SELECT query but not in the result set of the second SELECT query.

CHECK constraints in PostgreSQL allow us to specify Boolean conditions for inserting or updating values in one or more columns.

PostgreSQL offers a Pseudo-type known as SERIAL. It allows Postgres users to create auto-incremented columns in a table. Using SERIAL, you can create a sequence of integers.

The NOT NULL constraint ensures that the column accepts only non-null values. In Postgres, the CHECK constraint can be used as an alternative to the NOT NULL.

PostgreSQL offers a built-in mathematical function named ABS() that takes an expression as an argument and retrieves an absolute value for the specified number.

PostgreSQL offers several built-in math functions such as ROUND(), CEIL(), and FLOOR() to round a number up to specific decimal places.

PostgreSQL offers several commands to optimize, improve or maintain the health of a database, tables, etc., such as ANALYZE and VACUUM commands.

In Postgres, VACUUM is a command-line utility that vacates the space engaged by obsolete records, tuples, etc. It optimizes the performance of the Postgres databases, records, etc.