SQLite

## SQLite Expert Extension

This folder contains code for a simple system to propose useful indexes
given a database and a set of SQL queries. It works as follows:

  1. The user database schema is copied to a temporary database.

  1. All SQL queries are prepared against the temporary database. I
  1. All SQL queries are prepared against the temporary database.
     Information regarding the WHERE and ORDER BY clauses, and other query
     features that affect index selection, are recorded.
     features that affect index selection are recorded.

  1. The information gathered in step 2 is used to create (possibly a large
     number of) candidate indexes.
  1. The information gathered in step 2 is used to create candidate indexes
     - indexes that the planner might have made use of in the previous step,
     had they been available.

  1. A subset of the data in the user database is used to generate statistics
     for all existing indexes and the candidate indexes generated in step 3
     above.

  1. The SQL queries are prepared a second time. If the planner uses any
     of the indexes created in step 3, they are recommended to the user.

Or an entire text file worth of queries with:

<pre>
  ./sqlite3_expert -file &lt;text-file&gt; test.db
</pre>

By default, sqlite3_expert generates index statistics using all the data in
By default, sqlite3\_expert generates index statistics using all the data in
the user database. For a large database, this may be prohibitively time
consuming. The "-sample" option may be used to configure sqlite3_expert to
consuming. The "-sample" option may be used to configure sqlite3\_expert to
generate statistics based on an integer percentage of the user database as
follows:

<pre>
  # Generate statistics based on 25% of the user database rows:
  ./sqlite3_expert -sample 25 -sql &lt;sql-query&gt; test.db

  # Do not generate any statistics at all:
  ./sqlite3_expert -sample 0 -sql &lt;sql-query&gt; test.db
</pre>