title: SQL Select Time Difference Between VARCHAR Column Types
body: <p>I have a table in my database which has two columns, one <code>START_TIME</code> and the other <code>END_TIME</code>. The columns are of type <code>VARCHAR2</code>. </p>
  
  <p>I want to select the time difference between these two columns.</p>
  
  <p>Just to know what kind of data these columns contains I have selected the data from these columns below.</p>
  
  <p>This is the result of <code>SELECT DISTINCT start_time FROM table_name</code> :</p>
  
  <pre><code>15:20
  22.30
  16:00
  24:00
  07:00
  06:55
  6:45
  23:50
  6.5
  15.20
  19:00
  0:00
  1600
  16
  19
  15:00
  6:50
  7
  15:30
  23.50
  24
  14.75
  23
  15:45
  00:15
  </code></pre>
  
  <p>and this is the result of <code>SELECT DISTINCT end_time FROM table_name</code></p>
  
  <pre><code>07:00
  16:00
  24:00
  6:45
  15:35
  07
  00
  16
  08:00
  07:20
  7.25
  15:00
  0700
  7
  15:30
  15
  06:45
  07.00
  24
  15.30
  7:00
  23
  15:45
  00:15
  </code></pre>
  
  <p>What can be done?</p>