面试题与答案

PostgreSQL is an open-source relational database management system (RDBMS). It differs from others by its extensibility and support for SQL and procedural languages.

The PRIMARY KEY constraint uniquely identifies each record in a table and ensures data integrity.

INNER JOIN retrieves rows where there is a match in both tables, while LEFT JOIN retrieves all rows from the left table and matching rows from the right table.

A subquery is a query nested within another query, returning a single value or a set of values. JOIN combines rows from two or more tables based on a related column.

The EXPLAIN command shows the execution plan of a statement, helping to optimize queries by revealing how PostgreSQL processes them.

A view is a virtual table based on the result of a SELECT query. It does not store the data itself but provides a way to represent data stored in one or more tables. Unlike a table, a view does not store data physically.

Common indexing techniques include B-tree, Hash, and GiST indexes. They should be used to improve query performance, especially for columns frequently used in WHERE clauses or JOIN conditions.

VACUUM is used to reclaim storage occupied by dead tuples, while ANALYZE is used to update statistics about the distribution of data in a table, helping the query planner make better decisions.

The pg_hba.conf file controls client authentication, specifying which hosts are allowed to connect to the PostgreSQL server and how they can authenticate.

Normalization is the process of organizing data to eliminate redundancy and dependency, ensuring data integrity and reducing the likelihood of anomalies in a database.

Stored procedures are precompiled sets of one or more SQL statements stored in the database, while functions return a value and can be used in SQL queries like any other value.

The COPY command is used to copy data between a file and a table or between tables. It is a high-performance mechanism for bulk data loading.

A materialized view is a snapshot of a query result that is stored and can be queried like a table. It should be used when you need to precompute and store the results of a complex query for faster retrieval.

A hot standby is a replica that is actively applying changes from the primary server and is ready for failover. A warm standby is a replica that is not actively applying changes but can quickly take over in case of a primary failure.

The pg_stat_bgwriter view provides statistics about the background writer process in PostgreSQL, helping monitor and optimize the writing of dirty buffers to disk.