title: How to get sum of a column based on the values of two columns in SQL
body: <p>I have a table as bellow with 3 columns. Sample data is given</p>
  
  <pre><code>column_1    column_2    column_3
     A           a           10
     A           b           20
     B           a           10
     A           a           10
     B           a           30
     A           b           40
     A           c           10
     C           a           20   
  </code></pre>
  
  <p>I want to get the sum of column_3 based on the values of column_1 and column_2. Which means I want to get the sum of values in column_3 which are having 'A' for column_1 'a' for column_2 and so on..</p>
  
  <pre><code>Sample output is given bellow
       column_1    column_2    SUM(column_3)
         A           a              20
         A           b              60
         A           c              10
         B           a              40
         C           a              20        
  </code></pre>
  
  <p>Can someone please tell me how to do this</p>