Obtaining Query Count Without executing a Query in Oracle D2k
Obtaining a count of records that will be retrieved by EXECUTE_QUERY
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
for the corresponding block immediately following the COUNT_QUERY.
The following function does the job:
FUNCTION query_count (p_block_name VARCHAR2) RETURN NUMBER
cnt := GET_BLOCK_PROPERTY(p_block_name, QUERY_HITS);
IF FORM_SUCCESS THEN
MESSAGE('Error in getting Query Hits for block '||:SYSTEM.CURRENT_BLOCK);
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
v_cnt := query_count(<detail block name>);
IF (v_cnt = 0) THEN
p_show_alert('No Details exist.');
GO_BLOCK(<detail block name>);
This technique involves two tasks:
is necessary to initiate the QUERY_HITS
property of the block and should be immediately before the GET_BLOCK_PROPERTY
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