I have more than 30,000 rows in a table. It takes a lot of time to load all the data in the gridview. So I want to display 100 rows at a time. When I click next page button, another 100 rows should be displayed. When I click previous page button, previous 100 rows should be displayed. If I type page 5 in a text box, then I want to jump over to the 5th lot of rows.
I also want to display how many pages there will be. Can we implement this concept in vb.net [winform] gridview. I am using database PostgreSQL.
Can anybody give me a hint or some concept?
Look at OFFSET and LIMIT in PostgreSQL.
Your query for the 5th page could look like this:
SELECT *
FROM tbl
ORDER BY id
OFFSET 400
LIMIT 100;
id is the primary key in my example, therefore an index is in place automatically.
If you access the table a lot in this fashion, performance may profit from using CLUSTER.
Total number of pages:
SELECT ceil(1235::real / 100)::int
FROM tbl;
If you wanted the number rounded down, just simplify to:
SELECT 1235 / 100
FROM tbl;
With both numbers being integer the result will be an integer type and fractional digits truncated automatically. But I think you need to round up here.
Related
I'm using paging in my app but I've noticed that paging has gone very slow and the line below is the culprit:
SELECT COUNT (*) FROM MyTable
On my table, which only has 9 million rows, it takes 43 seconds to return the row count. I read in another article which states that to return the row count for 1.4 billion rows, it takes over 5 minutes. This obviously cannot be used with paging as it is far too slow and the only reason I need the row count is to calculate the number of available pages.
After a bit of research I found out that I get the row count pretty much instantly (and accurately) using the following:
SELECT SUM (row_count)
FROM sys.dm_db_partition_stats
WHERE object_id=OBJECT_ID('MyTable')
AND (index_id=0 or index_id=1)
But the above returns me the count for the entire table which is fine if no filters are applied but how do I handle this if I need to apply filters such as a date range and/or a status?
For example, what is the row count for MyTable when the DateTime field is between 2013-04-05 and 2013-04-06 and status='warning'?
Thanks.
UPDATE-1
In case I wasn't clear, I require the total number of rows available so that I can determine the number of pages required that will match my query when using 'paging' feature. For example, if a page returns 20 records and my total number of records matching my query is 235, I know I'll need to display 12 buttons below my grid.
01 - (row 1 to 20) - 20 rows displayed in grid.
02 - (row 21 to 40) - 20 rows displayed in grid.
...
11 - (row 200 to 220) - 20 rows displayed in grid.
12 - (row 221 to 235) - 15 rows displayed in grid.
There will be additional logic added to handle a large amount of pages but that's a UI issue, so this is out of scope for this topic.
My problem with using "Select count(*) from MyTable" is that it is taking 40+ seconds on 9 million records (thought it isn't anymore and I need to find out why!) but using this method I was able to add the same filter as my query to determine the query. For example,
SELECT COUNT(*) FROM [MyTable]
WHERE [DateTime] BETWEEN '2018-04-05' AND '2018-04-06' AND
[Status] = 'Warning'
Once I determine the page count, I would then run the same query but include the fields instead of count(*), the CurrentPageNo and PageSize in order to filter my results by page number using the row ids and navigate to a specific pages if needed.
SELECT RowId, DateTime, Status, Message FROM [MyTable]
WHERE [DateTime] BETWEEN '2018-04-05' AND '2018-04-06' AND
[Status] = 'Warning' AND
RowId BETWEEN (CurrentPageNo * PageSize) AND ((CurrentPageNo + 1) * PageSize)
Now, if I use the other mentioned method to get the row count i.e.
SELECT SUM (row_count)
FROM sys.dm_db_partition_stats
WHERE object_id=OBJECT_ID('MyTable')
AND (index_id=0 or index_id=1)
It returns the count instantly but how do I filter this so that I can include the same filters as if I was using the SELECT COUNT(*) method, so I could end up with something like:
SELECT SUM (row_count)
FROM sys.dm_db_partition_stats
WHERE object_id=OBJECT_ID('MyTable') AND
(index_id=0 or index_id=1) AND
([DateTime] BETWEEN '2018-04-05' AND '2018-04-06') AND
([Status] = 'Warning')
The above clearing won't work as I'm querying the dm_db_partition_stats but I would like to know if I can somehow perform a join or something similar to provide me with the total number of rows instantly but it needs to be filtered rather than apply to the entire table.
Thanks.
Have you ever asked for directions to alpha centauri? No? Well the answer is, you can't get there from here.
Adding indexes, re-orgs/re-builds, updating stats will only get you so far. You should consider changing your approach.
sp_spaceused will return the record count typically instantly; You may be able to use this, however depending (which you've not quite given us enough information) on what you are using the count for might not be adequate.
I am not sure if you are trying to use this count as a means to short circuit a larger operation or how you are using the count in your application. When you start to highlight 1.4 billion records and you're looking for a window in said set, it sounds like you might be a candidate for partitioned tables.
This allows you assign several smaller tables, typically separated by date, years / months, that act as a single table. When you give the date range on 1.4+ Billion records, SQL can meet performance expectations. This does depend on SQL Edition, but there is also view partitioning as well.
Kimberly Tripp has a blog and some videos out there, and Kendra Little also has some good content on how they are used and how to set them up. This would be a design change. It is a bit complex and not something you would want implement on a whim.
Here is a link to Kimberly's Blog: https://www.sqlskills.com/blogs/kimberly/sqlskills-sql101-partitioning/
Dev banter:
Also, I hear you blaming SQL, are you using entity framework by chance?
By user sorting I mean that as a user on the site you see a bunch of items, and you are supposed to be able to reorder them (I'm using jQuery UI).
The user only sees 20 items on each page, but the total number of items can be thousands.
I assume I need to add another column in the table for custom ordering.
If the user sees items from 41-60, and and he sorts them like:
41 = 2nd
42 = 1st
43 = fifth
etc.
I can't just set the ordering column to 2,1,5.
I would need to go through the entire table and change each record.
Is there any way to avoid this and somehow sort only the current selection?
Add another column to store the custom order, just as you suggested yourself. You can avoid the problem of having to reassign all rows' values by using a REAL-typed column: For new rows, you still use an increasing integer sequence for the column's value. But if a user reorders a row, the decimal data type will allow you to use the formula ½ (previous row's value + next row's value) to update the column of the single row that was moved. You
have got two special cases to take care of, namely if a user moves a row to the very beginning or end of the list. In that case, just use min - 1 rsp. max + 1.
This approach is the simplest I can think of, but it also has some downsides. First, it has a theoretical limitation due to the datatype having only double-precision. After a finite number of reorderings, the values are too close together for their average to be a different number. But that's really only a theoretical limit you should never reach in practical applications. Also, the column will use 8 bytes of memory per row, which probably is much more than you actually need.
If your application might scale to the point where those 8 bytes matter or where you might have users that overeagerly reorder rows, you should instead stick to the INTEGER column and use multiples of a constant number as the default values (e.g. 100, 200, 300, ..). You still use the update formula from above, but whenever two values become too close together, you reassign all values. By tweaking the constant multiplier to the average table size / user behaviour, you can control how often this expensive operation has to be done.
There are a couple ways I can think of to do this. One would be to use a SELECT FROM SELECT style statement. As in something like this.
SELECT *
FROM (
SELECT col1, col2, col3...
FROM ...
WHERE ...
LIMIT n,m
) as Table_A
ORDER BY ...
The second option would be to use temp tables such as:
INSERT INTO temp_table_A SELECT ... FROM ... WHERE ... LIMIT n,m;
SELECT * FROM temp_table_A ORDER BY ...
Another option to look at would be jQuery plugin like DataTables
one way i can think of is:
Add a new column (if feasible) or create a new table for holding the order of the items.
On any page you will show around 20 items based on the initial ordering.
Using the jquery's Draggable you can send updates to this table
I think you can do this with an extra column.
First, you could prepopulate this new column with a default sort order and then allow the user to interactively modify it with the drag and drop of jquery-ui.
Lets say this user has 100 items in the table. You set the values in the order column to [1,2,3,...,99,100]. I suggest that you run a script on the original table to set all items to a default sort order.
Now going back to your example where the user is presented with items 41-60: the initial presentation in their browser would rank those at orders [41,42,43,...,59,60]. You might also need to save the lowest order that appears in this subset, in this case 41. Or better yet, save the entire array of rankings and restore the exact same numbers in the new order. This covers the case where they select a set of records that are not already consecutively ordered, perhaps because they belong to someone else.
To demonstrate what I mean: when they reorder them in the page, your javascript reassigns those same numbers back to the subset in the new order. Like this:
item A : 41
item B : 45
item C : 46
item D : 47
item E : 51
item F : 54
item G : 57
then the user changes them to this order, but you reassign the numbers like this:
item D : 41
item F : 45
item E : 46
item A : 47
item C : 51
item B : 54
item G : 57
This should also work if the subset is consecutive.
I'm currently writing a stored procedure for my client to populate some tables that will be used to generate SSRS reports later on. Some of the data is based on specific stock formulas that are run on each of their clients' quarterly data (sent to them by their clients). The other part of the data is generated by comparing those results against those from other, similar sized clients. One of the things that they want tracked in their reports is the average of the top 25% of formula results for that particular comparison group.
To give a better picture of it, imagine the following fields that I have in a temp table:
FormulaID int
Value decimal (18,6)
I want to do the following: Given a specific FormulaID return the average of the top 25% of Value.
I know how to take an average in SQL, but I don't know how to do it against only the top 25% of a specific group.
How would I write this query?
I guess you can do something like this...
SELECT AVG(Q.ColA) Avg25Prec
FROM (
SELECT TOP 25 Percent ColA
FROM Table_Name
ORDER BY SomeCOlumn
) Q
Here's what I did, given the table shown above:
select AVG(t.Value)
from (select top 25 percent Value
from #TempGroupTable
where FormulaID = #PassedInFormulaID
order by Value desc) as t
The desc must be there, because the percent command will not actually do comparisons. It will just simply grab the first x number of records, with x being equal to 25% of the count of records it's querying. Therefore, the order by Value desc line then will grab the top 25% records which have the highest Value, and then sends that info to be averaged.
As a side note to all of this, this also means that if you wanted to grab the bottom 25% instead, or if your formula results are like a golf score (i.e. lowest is the best), all you would need to do is remove the desc part and you would be good to go.
How can I fill the page with empty table rows? For example; I have 2 records in the dataset but I want to the page with empty rows (draw the table borders until the end of page)
I have;
I want;
Are you getting your report data from a database? If so you might look at returning empty rows from your database call.
If you can describe your data source and query that you are using for this report, we might be able to suggest changes to the query to return blank rows.
UPDATE:
OK, Based on how you describe the data you are getting, perhaps you can change your database call to do something like this:
select * from Subeler where Subeler.FirmaId = 10
UNION ALL
select TOP 5 ' ' from Subeler where 1 = 1
That will give you your original data, plus 5 "blank" rows to help pad your report. Of course you would have to make sure the second query has the same number and type of columns as your first, but hopefully this will point you in the right direction.
basically i have albums, which has 50 images init.. now if i show list of images, i know from which to which row is showing (showing: 20 to 30 of 50), means showing 10 rows from 20 - 30. well now the problem is, i want to select an image, but still show which postion was it selected, so i can move back and forth, but keep the postion too.
like if i select 5th image, which id is 'sd564', i want to show (6 of 50 images), means you are seeing 6th of 50 images.. if i get next row id and show that, then, i want to show (7 of 50 images).
well i can do all this from pagination pointer easily, like in url say (after=5, after=6)... its moving with postion, but what if i dont have this (after=6) and just have an id, how can i still do that?
i dont want to use (after=6) also because its dynamic site and images adds and delete, so position chnages and sharing with someone else and going back on same old link, then it would be wrong position.
what kind of sql query should i be running for this?
currently i have
select * from images where id = 'sd564';
obviously i need to add limit or some other thing in query to get what i want or maybe run another query to get the result, while keeping this old query inplace too. anyway i just want positioning. i hope you can help me solve this
Example: http://media.photobucket.com/image/color%20splash/aly3265/converse.jpg
sample http://img41.imageshack.us/img41/5631/viewing3of8240.png
Album Query Request (check post below)
select images.* from images, album
where album_id = '5'
and album_id = image_album_id
order by created_date DESC
limit ....;
Assuming created_date is unique per album_id and (album_id,created_date) is unique for all rows in images, then this:
select i1.*, count(*) as position
from images i1
inner join images i2
on i1.album_id = i2.album_id -- get all other pics in this album
and i1.created_date >= i2.created_date -- in case they were created before this pic
where i1.album_id = 5
group by i1.created_date
will reliably get you the images and their position. Please understand that this will only work reliably in case (album_id,created_date) are unique throughout the images table. If that is not the case, the position wont be reliable, and you might not see all photos due to the GROUP BY. Also note that a GROUP BY clause like this, only listing some of the columns that appear in the SELECT list (in this case images.*) is not valid in most RDBMS-es. For a detailed discussion on that matter, see: http://dev.mysql.com/tech-resources/articles/debunking-group-by-myths.html
By doing this:
select i1.*, count(*) as position
from images i1
inner join images i2
on i1.album_id = i2.album_id -- get all other pics in this album
and i1.created_date >= i2.created_date -- in case they were created before this pic
where i1.album_id = 5
group by i1.created_date
having count(*) = 4
you select the image at the 4th position (note the having count(*) = 4)
By doing this:
select i1.*, count(*) as position
from images i1
inner join images i2
on i1.album_id = i2.album_id -- get all other pics in this album
and i1.created_date >= i2.created_date -- in case they were created before this pic
where i1.album_id = 5
group by i1.created_date
having count(*) between 1 and 10
you select all photos with positions 1 through 10 (note the having clause again.)
Of course, if you just want one particular image, you can simply do:
select i1.*, count(*) as position
from images i1
inner join images i2
on i1.album_id = i2.album_id -- get all other pics in this album
and i1.created_date >= i2.created_date -- in case they were created before this pic
where i1.image_id = 's1234'
group by i1.created_date
This will correctly report the position of the image within the album (of course, assuming that image_id is unique with in the images table). You don't need the having clause in that case since you already pinpointed the image you want.
From what you are saying here:
dont want to use (after=6) also because its dynamic site and images adds and delete, so position chnages and sharing with someone else and going back on same old link, then it would be wrong position.
I get the impression that this is not a SQL problem at all. The problem is that the positions of the fotos are local to the search resultset. To reliably naviate by position, you would need to make a snapshot (no pun intended) of some kind. That is, you need to have some way to "freeze" the dataset while it is being browsed.
A simple way to do it, would be to execute the search, and cache the result outside of the actual current datastore. For example, you could use "scratch tables" in your database, simply store it in temporary files, or in some memory caching layer if you have the mem for it. With this model, you'd let the user browse the resultset from the cache, and you would need to clean out the cache when the user's session ends (or after some timeout, you don't want to kill your server because some users don't log out)
Another way to do it, is to simply allow yourself to lie now and then. Let's say you have result pages of 10 images, and a typical search delivers 50 pages of results. Well, you could simply send a resultset for a fixed number of items, say 100 photos (so 10 pages) to the client. These search results would then be your snapshot, and contain references to the actual pictures. If you are storing the URLS in the database , and not the binary data, this reference is simply the URL. Or you could store the database Id there. Anyway, the user is allowed to browse the initial resultset, and chances are that they never browse the entire set. If they do, you re-execute the query on the server side for the next chunk of pages. If many photos were added in the mean time that would end up at positions 1..100, then the user will see stale data: that's the price they pay for having so much time on their hands that they can allow themselvs to browse 10 pages of 10 photos.
(of course, you should tweak the parameters to your liking but you get the idea I'm sure.)
If you don't want to 'lie' and it is really important that people can reliably browse all the results they searched, you could extend your database schema to support snapshots at that level. Now asssuming that there are only two operations for photos, namely "add" and "delete", you would have a TIMESTAMP_ADDED and a TIMESTAMP_REMOVED in your photo table. On add, you do the INSERT in your db, and fill TIMESTAMP_ADDED with the currrent timestamp. The TIMESTAMP_REMOVED would be filled with the theoretical maximum value for whatever data type you like to use to store the timestamp (For this particular case I would probably go for an INT column and simply store the UNIX_TIMESTAMP) On delete, you don't DELETE the row from the db, rather, you mark it as deleted by updating TIMESTAMP_REMOVED column, setting it to the current timestamp. Now when you have to do a search, you use a query like:
SELECT *
FROM photo
WHERE timestamp_added < timestamp_of_initial_search
AND timestamp_removed > timestamp_of_initial_search
AND ...various search criteria...
ORDER BY ...something
LIMIT ...page offset and num items in page...
The timestamp_of_initial_search is the timestamp of executing the initial search for a particular set of criteria. You should store that in the application session while the user is browsing a particular search resultet so you can use that in the subsequent queries required for fetching the pages. The first two WHERE criteria are there to implement the snapshot. The condition timestamp_added < timestamp_of_initial_search ensures we can only see photos that were added before the timestamp of executing the search. The condition timestamp_removed > timestamp_of_initial_search ensures we only search that were not already removed by the time the initial search was executed.
Of course, you still have to do something with the photos that were marked for delete. You could schedule periodical physical deletion for all photos that have a timestamp removed that is smaller than any of the current search resultsets.
If I understood your problem correctly, you can use the Row_Number() function (in SQL Server). To get the desired result, you can use a query something similar to this:
select images1.* from
(SELECT ROW_NUMBER() OVER (ORDER BY image_album_id) as rowID,(SELECT COUNT(*) FROM images) AS totCount, * FROM images) images1
JOIN album ON (album_id = images1.image_album_id)
where album_id = '5'
order by images1.image_album_id
limit ....;
Here the images.rowid gives you the position of the row and images.totCount give you the total number of rows.
Hope it helps.
Thnks.