title: ORA-00937: not a single-group group function PROBLEM
body: <p>I'm trying to find the number of transaction per value   bend analysis for following for each of trans type per the BRACKTS : 1-100 , 101-200</p>
  <pre><code>SELECT TO_CHAR(TRANSDATE,'MM-YY') MONTH 
  , AGENT_NUMBER 
  , COUNT(DISTINCT RECEIVER) NUM_OF_CUST 
  , COMMAND_ID 
  , BRACKETS 
  FROM (
      SELECT TRANSDATE 
      , AGENT_NUMBER 
      , RECEIVER 
      , COMMAND_ID 
      , CASE 
        WHEN COUNT(DISTINCT RECEVIVER) BETWEEN 1 AND 100 THEN '1-100' , 
        WHEN COUNT(DISTINCT RECEIVER) BETWEEN 101 AND 200 THEN '101-200' 
        ELSE '0' END BRACKETS 
      FROM TRANSACTION@ABSDB 
      WHERE RESULT_CODE = 'DONE' 
      AND TO_CHAR (TRANSDATE,''MM-YY) = '06-21')
  GROUP BY  TO_CHAR(TRANSDATE,'MM-YY') 
          , AGENT_NUMBER  , COMMAND_ID , BRACKETS 
  </code></pre>