title: Indexing column for full text search
body: <p>I have column <code>col</code> with data type <code>CHARACTER VARYING</code></p>
  
  <p>I need that index this column as <code>gin</code> index. If trying directly set gin index to column, returned error:  </p>
  
  <p><code>data type character varying has no default operator class for access method "gin"
  HINT:  You must specify an operator class for the index or define a default operator class for the data type</code></p>
  
  <p>If trying:  </p>
  
  <pre><code> create index col_vector 
   on mytable 
   using gin (to_tsvector(col))
  </code></pre>
  
  <p>I got error:  <code>functions in index expression must be marked IMMUTABLE</code></p>
  
  <p>How to create <code>gin</code> index for <code>CHARACTER VARYING</code> column ?</p>
  
  <p>p.s. I need this for full text search</p>