title: How to find a column with null and not null values in same table
body: <p>I have a table where I need to find a column with null and not null values. for e.g. The column has a value today but becomes null tomorrow. </p>
  
  <p>First Query:</p>
  
  <pre><code>select * from test where Account Number is Not Null and LastChangedDate is Null  
  </code></pre>
  
  <p>But this query brings the records with null values and not listing the records with values for LastChangedDate column</p>
  
  <p>Below is the sample record</p>
  
  <pre><code>AccountNumber EffectiveDate LastChangedDate 
  1234567     2019-05-31          2018-09-14
  1234567     2019-06-30          2018-09-14
  1234567     2019-07-31           NULL
  </code></pre>
  
  <p>Second query:</p>
  
  <pre><code>select * from test where Account Number is Not Null and 'LastChangedDate' is Null  
  </code></pre>
  
  <p>But this query brings the records with null values and not listing the records with values for 'LastChangedDate' column</p>
  
  <p>Expected: Able to retrieve all records for same column with Null and Not Null values and omit the records with all values populated</p>