A subquery (also known as a nested query or inner query) is a query that is embedded within another query. Subqueries are used to retrieve data that will be used in the main query’s conditions, expressions, or selection criteria. They are a powerful tool for combining multiple queries and performing more complex operations in a…
The EXCEPT keyword is used in a query to retrieve distinct rows from the result of the first query that are not present in the result of the second query. In other words, it returns the set difference between the results of two queries. The basic syntax of the EXCEPT operator is as follows: SELECT…
The GROUPING SETS operation is used in conjunction with the GROUP BY clause to generate a result set that includes aggregated data for multiple specified groups of columns. It’s a way to efficiently achieve the same effect as using multiple GROUP BY clauses separately. The basic syntax of using GROUPING SETS in a query is…
The ROLLUP operation is used in conjunction with the GROUP BY clause to generate a result set that includes aggregated data for various levels of a specified grouping columns hierarchy. It’s similar to the CUBE operation, but it provides a more structured way of obtaining summary data for different hierarchical levels. The basic syntax of…
The CUBE operation is used in conjunction with the GROUP BY clause to generate a result set that includes aggregated data for all possible combinations of specified grouping columns. It’s a powerful way to perform multi-dimensional analysis and obtain summary data for various dimensions simultaneously. The basic syntax of using CUBE in a query is…
The NATURAL JOIN is a type of join that automatically matches columns with the same name in two or more tables and combines the rows where those columns have matching values. Essentially, a NATURAL JOIN performs an INNER JOIN using the columns with the same names as the join criteria. The basic syntax of a…
A CROSS JOIN, also known as a Cartesian Join, is used to combine all rows from two or more tables, producing a result set where each row from the first table is combined with every row from the second table, and so on. Unlike other types of joins, CROSS JOIN does not require a join…
A FULL OUTER JOIN is used to retrieve data from two or more tables based on a specified condition, including all rows from both the left (or first) table and the right (or second) table. If there’s no match for a row in one table, the columns from the other table will be filled with…
A self-join in PostgreSQL is a type of join operation where a table is joined with itself. This is often used when you have a single table that contains related data that you want to compare or analyze within the same table. To perform a self-join, you treat the table as if it were two…
A RIGHT JOIN is used to retrieve data from two or more tables based on a specified condition, while also including all the rows from the right (or second) table, even if there is no match in the left (or first) table. This means that even if there is no matching row in the left…