What's the difference between MyISAM and InnoDB

The main differences between InnoDB and MyISAM  "with respect to designing a table or database" you asked about  are support for "referential integrity" and "transactions".
If you need the database to enforce foreign key constraints, or you need the database to support transactions (i.e. changes made by two or more DML operations handled as single unit of work, with all of the changes either applied, or all the changes reverted) then you would choose the InnoDB engine, since these features are absent from the MyISAM engine.
Those are the two biggest differences. Another big difference is concurrency. With MyISAM, a DML statement will obtain an exclusive lock on the table, and while that lock is held, no other session can perform a SELECT or a DML operation on the table.

Key Differences :

MYISAM: MYISAM supports Table-level Locking MyISAM designed for need of speed MyISAM does not support foreign keys hence we call MySQL with MYISAM is DBMS MyISAM stores its tables, data and indexes in diskspace using separate three different files. (tablename.FRM, tablename.MYD, tablename.MYI) MYISAM not supports transaction. You cannot commit and rollback with MYISAM. Once you issue a command it’s done. MYISAM supports fulltext search You can use MyISAM, if the table is more static with lots of select and less update and delete. INNODB: InnoDB supports Row-level Locking InnoDB designed for maximum performance when processing high volume of data InnoDB support foreign keys hence we call MySQL with InnoDB is RDBMS InnoDB stores its tables and indexes in a tablespace InnoDB supports transaction. You can commit and rollback with InnoDB