What is the purpose of using pgsql explain?

EXPLAIN is a keyword in PostgreSQL that is used to analyze the execution plan of query statements. Its purpose is to show the steps and methods taken by the PostgreSQL query optimizer when executing a query, as well as the various costs and statistical information needed to actually run the query.

Specifically, the functions of EXPLAIN include:

1. Plan analysis query: Display the execution plan of a query in the database, including the indexes used, the join methods, filtering conditions, etc., to help users understand the query performance bottlenecks and optimization opportunities.
2. Performance optimization: By examining the execution plan, potential performance issues can be identified and query statements or database structures can be optimized accordingly to improve query efficiency.
3. The statistics provided by EXPLAIN will include estimated row counts, costs, actual execution details for each table in the query, which helps in assessing the complexity and resource consumption of the query.
4. Debugging tool: As a debugging tool, you can use EXPLAIN to view the internal workings of a query during execution, helping to identify and troubleshoot issues.

In conclusion, EXPLAIN is a very useful tool in PostgreSQL that can help database administrators and developers gain insight into query execution details, ultimately optimizing query performance and improving overall database performance.