title: Updating Multiple Columns with multiple Joins
body: <p>I'm receiving some data from an external source, where the actual values are replaced with ids.</p>
  
  <pre><code>| Serial# | Sex | Married | Income |
  ------------------------------------
  |    1    |  1  |    2    |   1    |
  |    2    |  1  |    1    |   3    |
  |    3    |  1  |    2    |   2    |
  </code></pre>
  
  <p>Now, I've a Dimension table with the values for each id:</p>
  
  <pre class="lang-none prettyprint-override"><code>| Tag     |        Value        | Id |
  --------------------------------------
  | Sex     |  M                  | 1  |
  | Sex     |  F                  | 2  |
  | Married |  Y                  | 1  |
  | Married |  N                  | 1  |
  | Income  |  Less than 100      | 1  |
  | Income  |  Between 100 and 1K | 2  |
  | Income  |  More than 1K       | 3  |
  </code></pre>
  
  <p>Now, I want all the ids of the three columns Sex, Married &amp; Income in the First table to be replaced with the values from the First Table.</p>
  
  <p>Also, if a unknown Id comes in, which is not present in the Dimension Table, we would love to update with 'UNKNOWN'</p>
  
  <p>This is just an example. My data contains ~100 such columns.
  What will be the cheapest and fastest way to achieve that?
  I don't want to write 100s of UPDATE statements.</p>