What is HEAP table in MySql

Heap table also known as Memory Storage Engine. Heap table is a special table with contents that are stored in memory because the data is vulnerable to crashes, hardware issues, or power outages, only use these tables as temporary work areas or read-only caches for data pulled from other tables.

Heap table are usually used for high-speed temprory storage.No TEXT or BLOB fields are allowed within Heap table.you can only use the comparision operators = and <=>.Heap table do not support auto-increment indexes  must be NOT NULL.