title: Comparing strings in postgres using comparison operators?
body: <p>In many programming languages you can compare strings using operators like >, >=, &lt; etc...and the language will base the comparison on the position of the letter in the alphabet.</p>
  
  <p>For example in PHP</p>
  
  <pre><code>if ('a' &lt; 'b') {
      echo 'Yes';
  } else {
      echo 'No';
  }
  &gt; Yes
  </code></pre>
  
  <p>However in postgres or mysql</p>
  
  <pre><code>SELECT
  CASE WHEN 'a' &lt; 'b' THEN 'yes' END
  FROM table
  Output: null
  </code></pre>
  
  <p>I have a table with strings that I need to compare against each other through SQL.</p>
  
  <p>For example:
  6.2(5a) 
  6.2(5b) -- this would be greater than 6.2(5a)
  Or 
  6.2(15) -- this would be greater than 6.2(5a)</p>
  
  <p>I thought of assigning a number to a letter using a regexp but then that would break the comparisons when there are no letter.</p>
  
  <p>How would you go about this purely in SQL?</p>