title: In SQL how to not select rows where a column value is the same as the one in the row above it
body: <p>I have a table with column Value and Timestamp. The values keep coming in per second. So I would have data as follows</p>
  
  <pre><code>V1 T1
  V1 T2
  V2 T3
  V3 T4..
  </code></pre>
  
  <p>etc.. So The timestamps would keep increasing, but the values can be the same that they don't change.
  I want to select only the rows where the value is different than the previous row.
  So I want to reduce the data and select only the records where there is a change in the data. 
  Would anybody know how to do this?</p>