Q:

Analog of "Index-only scans" from PostgreSQL in MySQL

When analyzing PostgreSQL query execution plans for some queries you can exploit Index-only scans:

Index-only scans are a major performance feature added to Postgres 9.2. They allow certain types of queries to be satisfied just by retrieving data from indexes, and not from tables.

Is there something similar you can use in MySQL?

A:

It's funny that you want something like Postgres index-only scans in Mysql.
Because there are this feature in Mysql long before the Postgres 9.2. But in mysql this feature called covering index:

An index that includes all the columns retrieved by a query. Instead
  of using the index values as pointers to find the full table rows, the
  query returns values from the index structure, saving disk I/O. InnoDB
  can apply this optimization technique to more indexes than MyISAM can,
  because InnoDB secondary indexes also include the primary key columns.
  InnoDB cannot apply this technique for queries against tables modified
  by a transaction, until that transaction ends.
Any column index or composite index could act as a covering index,
  given the right query. Design your indexes and queries to take
  advantage of this optimization technique wherever possible.

