Why is the vertical Scrollbar on a TDBGrid not displayed?

Question

I have two DB grids on a form and one has a vertical scrollbar and the other doesn't, even when the DataSource query returns more results than the Grid's visible rows.

Why is the vertical scrollbar on the TDBGrid not displayed?

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[Update] Delphi XE2 starter, using AnyDac.

When I first start the program, the DB grid does have a vertical scrollbar, but later it vanishes and I have narrowed it down, but still cannot understand how to correct teh problem.

I have two MySql tables and two DBgrids. One is an overview of all test runs and the other contains details of measurements taken during a test run. When the user clicks on a row of the "summary" grid, I update a parameter of the query of the "details" grid. This works and does not remove the scroll bar.

The problem comes when I start a new tets run and insert a new row into the "summary" table - the scroll bar of the "details" table vanishes!

mysql> describe test_runs;
+------------------+-------------+------+-----+-------------------+----------------+
| Field            | Type        | Null | Key | Default           | Extra          |
+------------------+-------------+------+-----+-------------------+----------------+
| run_id           | int(11)     | NO   | PRI | NULL              | auto_increment |
| start_time_stamp | timestamp   | NO   |     | CURRENT_TIMESTAMP |                |
| end_time_stamp   | timestamp   | YES  |     | NULL              |                |
| description      | varchar(64) | YES  |     | NULL              |                |
+------------------+-------------+------+-----+-------------------+----------------+
4 rows in set (0.02 sec)

mysql> describe measurements;
+------------------------+-----------+------+-----+-------------------+-------+
| Field                  | Type      | Null | Key | Default           | Extra |
+------------------------+-----------+------+-----+-------------------+-------+
| run_id                 | int(11)   | NO   | MUL | NULL              |       |
| measurement_time_stamp | timestamp | NO   |     | CURRENT_TIMESTAMP |       |
| ph                     | float     | NO   |     | NULL              |       |
| conductivity           | float     | NO   |     | NULL              |       |
| cod                    | float     | NO   |     | NULL              |       |
+------------------------+-----------+------+-----+-------------------+-------+
5 rows in set (0.04 sec)

mysql>

The AnyDac queries are, repectively,

SELECT 
   run_id,
   start_time_stamp,
   end_time_stamp,
   CONCAT(CONCAT(CONCAT(CONCAT(LPAD(EXTRACT(HOUR FROM timediff(end_time_stamp,start_time_stamp)), 2, '0'), ":"),LPAD(EXTRACT(MINUTE FROM timediff(end_time_stamp,start_time_stamp)), 2, '0'), ":"), LPAD(EXTRACT(SECOND FROM timediff(end_time_stamp,start_time_stamp)), 2, '0'))) AS duration,
   description    
FROM 
   test_runs 
ORDER BY 
   start_time_stamp 
DESC

and

SELECT 
   run_id,
   measurement_time_stamp, 
   ROUND(ph, :float_precision) as ph, 
   ROUND(conductivity, :float_precision) as conductivity, 
   ROUND(cod, :float_precision) as cod    
FROM 
   measurements    
WHERE 
   run_id=:run_id
ORDER BY 
   measurement_time_stamp 
DESC

As you can see, there is referce in the measurements table to the test_runs table

When I execute the following SQL, the scroll bar of the measurements table vanishes:

INSERT INTO 
   test_runs (start_time_stamp, description) 
VALUES 
   (CURRENT_TIMESTAMP, "<Currently running test>"); 

SELECT LAST_INSERT_ID() AS run_id

Can anyne tell me what I am doing wrong? Thanks a 0x000F4240

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[Update] Once again, the problem is that when I add a row to the test_runs table, the vertical scroll bar of the DB grid which reflects the query of the measurements table vanishes.

So, somehow, one DB grid/dataset/table is affecting the otherDB grid.

The data in the actual MySql database are fine. The problem occurs no matter whether I use a command to INSERT INTO and two decicated queries (with SQL fixed at design time and never changed) or if I use @kobik suggestion to dataset.append.

The database contents are fine, the DB contents are correct, when I click on the summary test_runs DB grid the contents of the details measurements DB grid are correctly updated.

The only problem is that inserting a row into the table of the test_runs query causes the scroll bar to vanish from the DB grid of the measurements DB grid.

When I comment that out, I can click the test_runs DB grid and swap between test runs without the scroll bar vanshing, but can never get back to the current test, because there is no entry for it in the DB grid.

When I first start a new test dataset.RecordCount` is, of course, zero - which might cause the scrollbar to vanish?

However, as measurements are made (every one second, timer based), I have checked and the value of dataset.RecordCount` increments, so here ought to be a scrollbar after the second measurement? Or do I have to force it to appear once the control has decided that it was not needed? (Invalidating the DB grid did not cause the missing scrollbar to appear)

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[Update] As suggested by @kobik I have made run_id a primary, auto increment key on the test_runs table and an index on the measurements table. I have updated the table details given above. I have also set the mastersource of the query which populates the test drun DB grid to the datasource of the test runs "summary" DB grid's query.

I delete the databse (my code auotmatically recreates it on first run). At first, neither DB grid had a vertical scroll bar, becaus they were both empty. When I added a first test the "summary" DB grid had no scroll bar, because it had only 1 entry, the "details" DB grid had no scrollbar at 0 and entries and the scroll bar appeared with the 2nd set of measurements.

I added a second test run and the "sumamry" DB grid had a scroll bar as it now had two entries, but as soon as I added the second entry to the summary, the scroll bar vanished from the "details" DB grid (which it did not do when there was a single test run), no matter how many entries it had (I breakpoint as each set of measuements is added and check measurementsQuery.RecordCount and see it go 0, 1, 2 ...)

It is worth pointing out that this only happens when I add a new test run (other than the first)). If I launch the program, both DB grids have scroll bars as expectd (> 1 entries). And I can click or mousewheel through the summary to disaply the details of the coresponding test run. The scroll bar never vanishes - until I add a new test run, which inserts a row ito the summary DB grid.

[Update]
Please see https://stackoverflow.com/questions/15399769/why-is-the-vertical-scrollbar-on-a-tdbgrid-not-displayed-redux

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Answer 1

After reading your comments, and reviewing your edit question, I'm pretty sure that the TDBGrid's "details" DataSet is returning a single record after your INSERT. And that explains why there is no vertical scrollbar - TDBGrid will show a vertical scrollbar only if records > 1.

You can make a simple test by checking the DataSet.RecordCount that is linked to the grid. It should show 1.

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Apparently, there is a known issue in QC: TDBGrid vertical scrollbar dissappears.
It goes all the way from D7..XE2. (Maybe even for older/newer versions).

When you have a master/detail record, and the detail is shown using a TDBGrid, then the vertical scrollbar dissappear randomly, even if there are more records than will fit! You can see the right border outline of the scrollbar though, including the thumb thingy moving. It's as if the grid has resized slightly over the scrollbar.

This might be true also for filtered DataSets.
So, You might want to implement one of the workarounds suggested in the QC.

Answer 2

I set the Scrollbars to ssBoth. It got fixed