title: VARCHAR type being converted incorrectly to ActiveRecord::Type::Value or ActiveRecord::Type::Decimal with mysql adapter
body: <p>Here is what I do to end up with the wrong ActiveRecord types.</p>
  
  <p>First, the schema of the table:</p>
  
  <pre><code>Field       | Type
  ------------------------------
  id          | int(10) unsigned
  user_name   | varchar(255)
  </code></pre>
  
  <p>Here is the code I tried in irb:</p>
  
  <pre><code>require 'active_record'
  ActiveRecord::Base.establish_connection(adapter: 'mysql', host: 'mrom.akamai.com', username: 'SOME_USER', password: 'SOME_PASSWORD', database: 'mrom_v3')
  c=ActiveRecord::Base.connection
  r = c.exec_query("select id, user_name, 'fixed string' value from user limit 2")
  t = r.column_types
  
  =&gt; {"id"=&gt;#&lt;ActiveRecord::Type::Integer:0x007fc144a5ed00 @precision=nil, @scale=nil, @limit=nil, @range=-2147483648...2147483648&gt;, "user_name"=&gt;#&lt;ActiveRecord::Type::Value:0x007fc144113f20 @precision=nil, @scale=nil, @limit=nil&gt;, "value"=&gt;#&lt;ActiveRecord::Type::Decimal:0x007fc144113e30 @precision=nil, @scale=nil, @limit=nil&gt;} 
  </code></pre>
  
  <p>Notice the ::Value and ::Decimal types for the user_name and value columns. I was expecting String.</p>
  
  <p>How can I fix this?</p>