No need to create an index on a column with a UNIQUE constraint, right?
<p>I have a table with three columns.</p>

<pre><code>_id (primary key)    word (unique)     frequency
</code></pre>

<p>In <a href="https://github.com/stephencelis/SQLite.swift/blob/master/README.md" rel="noreferrer">SQLite.swift</a> I create the table like this</p>

<pre class="lang-swift prettyprint-override"><code>try db.run( userDictionary.create(ifNotExists: true) {t in
    t.column(wordId, primaryKey: true)
    t.column(word, unique: true)
    t.column(frequency, defaultValue: 1)
    })
</code></pre>

<p>I believe the SQLite syntax that would be </p>

<pre class="lang-sql prettyprint-override"><code>CREATE TABLE "words" (
    "_id" INTEGER PRIMARY KEY NOT NULL,
    "word" TEXT UNIQUE NOT NULL,
    "frequency" INTEGER DEFAULT 1
)
</code></pre>

<p>I was preparing to add an index on the "word" column to speed up performance since I will have to do frequent queries on it. But then I read the following interesting statement in the <a href="http://www.tutorialspoint.com/sqlite/sqlite_indexes.htm" rel="noreferrer">Indexes tutorial by TutorialsPoint</a>:</p>

<blockquote>
  <p>Implicit Indexes:</p>
  
  <p>Implicit indexes are indexes that are automatically created by the
  database server when an object is created. <strong>Indexes are automatically
  created for primary key constraints and unique constraints.</strong></p>
</blockquote>

<p>So since I already added a unique constraint to the "word" column, there is no need to do anything else. Is that correct? I tried to confirm this in the <a href="https://www.sqlite.org/lang_createindex.html" rel="noreferrer">SQLite documentation</a> but I couldn't find it.</p>