Mysql

SQL Transaction Isolation Levels Transaction isolation levels define the degree to which the operations in one transaction are visible to other concurrent transactions and the types of reads and writes that are allowed. Comparison Table Isolation Level Dirty Read Non-repeatable Read Phantom Read READ UNCOMMITTED Yes Yes Yes READ COMMITTED No Yes Yes REPEATABLE READ No No Yes SERIALIZABLE No No No Explanation of Isolation Levels 1. READ UNCOMMITTED This is the lowest isolation level. [Read More]

What are the main MySQL storage engines and their differences? MySQL supports multiple storage engines, each with distinct characteristics: InnoDB: Default engine since MySQL 5.5 Supports ACID transactions Provides row-level locking Supports foreign keys and relationship constraints Uses clustered indexes MyISAM: Older engine, used as default before MySQL 5.5 Non-transactional Table-level locking Faster for read-heavy operations Supports full-text indexing Memory (HEAP): Stores data in RAM for fast access Non-persistent (data lost on restart) Useful for temporary tables and caches Archive: [Read More]

Input Tables INNER JOIN INNER JOIN returns only the rows where there’s a match between both tables based on the join condition. SELECT A.ID, A.Name, B.ID, B.Department FROM A INNER JOIN B ON A.ID = B.ID LEFT JOIN LEFT JOIN returns all rows from the left table (A), and the matched rows from the right table (B). If there’s no match, NULL values are used for the right table columns. [Read More]