What does it mean to rebuild an index When should this be do

What does it mean to rebuild an index? When should this be done in MySQL.

Solution

Reduild or coalesce an existing index is a process of Altering indexs.For this your schema must contain the index or you must have the ALTER ANY INDEX system privilege.

Reduild an index is require when they become highly fragmented by special events in database.Example, you perform a large, bulk load of data into an indexed table.