Q: How many engines in mysql ?

mysql> SHOW ENGINES;

nnoDB   
MRG_MYISAM
BLACKHOLE 
CSV       
MEMORY
FEDERATED
ARCHIVE  
MyISAM 

When to use MyISAM?
MyISAM is designed with the idea that your database is queried far more than its updated and as a result it performs very fast read operations. If your read to write(insert|update) ratio is less than 15% its better to use MyISAM.

MyISAM limitations

• No Foriegn keys and cascading deletes and updates
• No rollback abilities
• No transactional integrity (ACID compliance)
• Row limit of 4,284,867,296 rows
• Maximum of 64 indexes per row

·         When to use InnoDB?

·         InnoDB uses row level locking, has commit, rollback, and crash-recovery capabilities to protect user data. It supports transaction and fault tolerance

InnoDB Limitations

• No full text indexing
• Cannot be compressed for fast, read-only

Convert from one type of engine to other.

CREATE TABLE table_name (rid INT) ENGINE = INNODB;

CREATE TABLE table_name (rid INT) TYPE = INNODB