Obtaining Query Count Without executing a Query in Oracle D2k

Obtaining Query Count Without executing a Query in Oracle D2k

Obtaining a count of records that will be retrieved by  EXECUTE_QUERY  before  actually performing it in a database block is especially useful when the requirement is to   prevent navigation to a block when   query hits are zero. A typical scenario of such a situation is when the detail block records exist on a separate canvas not visible on Form startup and the user is required to click a Details button to see them. Giving an alert message such as  No Details exist  when the user clicks the Details button is more meaningful than displaying a blank details screen, when no details exist for the chosen parent record.

The technique given here avoids two performance issues. First, you do not want to perform a  SELECT COUNT(*)  from the corresponding base table mainly for performance reasons. Second, using  :SYSTEM.LAST_QUERY   and executing it dynamically using  DBMS_SQL  cause a bottleneck by executing   the query on the server side explicitly, thus involving more trips.

The solution is to do  a  COUNT_QUERY  and get  the  QUERY_HITS  for the corresponding block immediately following the  COUNT_QUERY.  The following function does the job:

 

FUNCTION query_count (p_block_name VARCHAR2) RETURN NUMBER

IS

cnt NUMBER;

BEGIN

GO_BLOCK(p_block_name);

COUNT_QUERY;

cnt := GET_BLOCK_PROPERTY(p_block_name, QUERY_HITS);

IF FORM_SUCCESS THEN

    RETURN (cnt);

ELSE

     MESSAGE('Error in getting Query Hits for block '||:SYSTEM.CURRENT_BLOCK);

     RAISE FORM_TRIGGER_FAILURE;

END IF;

END;

The preceding function can be called in the appropriate trigger, such as   WHEN-BUTTEN-PRESSED,  to achieve the desired functionality.

The following  WHEN-BUTTON-PRESSED  trigger is defined for the Details button. It initially invokes the above  query_count  function to obtain the count of detail records for a particular master record.   If this count is zero it throws an alert to indicate   No Details exist.  Otherwise, control navigates to the detail block and does an  EXECUTE_QUERY.

 

WHEN-BUTTON-PRESSED trigger of 'Details'button



DECLARE

   v_cnt NUMBER;

BEGIN

   v_cnt := query_count(<detail block name>);

   IF (v_cnt = 0) THEN

     p_show_alert('No Details exist.');

   ELSE

     GO_BLOCK(<detail block name>);

     EXECUTE_QUERY;

   END IF;

END;

This technique involves two tasks:

• COUNT_QUERY  is necessary to initiate the   QUERY_HITS  property of the block and should be immediately before the  GET_BLOCK_PROPERTY  statement.
• Oracle Forms displays the message FRM-40355:  Query will display 0 records  when the query hits are zero as obtained by a call to  COUNT_QUERY.  This should be suppressed in an  ON-MESSAGE  trigger by using the following code:
   

  if message_type = 'FRM'and message_code = 40355 then
  
     null;
  
  else
  
    message(message_type||'-'||to_char(message_code)||': '||message_text);
  
  end if;