title: Replace null value with previous available value in Row SQL server query
body: <p>I am looking for building a query to replace null value with previous available values.can somebody help.Here is the table currently looking like</p>
  
  <pre><code>11/30/2015   ID1     CLassName   1
  NULL         ID1     CLassName   2
  NULL         ID1     CLassName   3
  NULL         ID1     CLassName   4
  11/30/2015   ID1     CLassName   5
  NULL         ID1     CLassName   6
  NULL         ID1     CLassName   7
  12/31/2015   ID1     CLassName   1
  NULL         ID1     CLassName   2
  NULL         ID1     CLassName   3
  NULL         ID1     CLassName   4
  12/31/2015   ID1     CLassName   5
  NULL         ID1     CLassName   6
  NULL         ID1     CLassName   7
  </code></pre>
  
  <p>Output shall look like</p>
  
  <pre><code>11/30/2015       ID1     CLassName   1
  11/30/2015       ID1     CLassName   2
  11/30/2015       ID1     CLassName   3
  11/30/2015       ID1     CLassName   4
  11/30/2015       ID1     CLassName   5
  11/30/2015       ID1     CLassName   6
  11/30/2015       ID1     CLassName   7
  12/31/2015       ID1     CLassName   1
  12/31/2015       ID1     CLassName   2
  12/31/2015       ID1     CLassName   3
  12/31/2015       ID1     CLassName   4
  12/31/2015       ID1     CLassName   5
  12/31/2015       ID1     CLassName   6
  12/31/2015       ID1     CLassName   7
  </code></pre>