I have a strange situation with a select. I've noticed that when I select top 100, a record is not returning from the database, but when doing top 101 the record appears on position 41.
The query is like this:
select top 100 GroupId, count(HouseId)
from House h
group by h.GroupId
order by max([DateCreated]) desc
From all discussions about top 100 vs top 101 I've noticed that everybody is saying that the top 101 is using another algorithm and we can have a speed problem, but my problem is not about this. With top 100 I'm missing a record that should appear at index 41. Has anybody noticed something like this?
when you use
order by max([DateCreated]) desc
it is calculated before TOP in the query.
Every time you include one more record, max([DateCreated]) re-positions this new record according to its value among all other records.
The only way this makes sense to me is if you have a lot of records with the same max([DateCreated]). What do you get when you run this:
select top 100 with ties GroupId, count(HouseId)
from House h
group by h.GroupId
order by max([DateCreated]) desc
If you get more than 100 records, then the database was just picking the first 100 rows it got to after sorting the result set. When you changed it to TOP 101, another row was added and it probably ended up at row 41 due to clustered indexes or other query engine implementation details that might affect row order when the query isn't deterministic.
Related
I'm using AdventureWorks2019 to practise. I want to select top 10 values of FirstName column inside Person.Person table, after getting the values, I want to sort them by ascending.
When I've tried to select top 10 values, I've got result:
Syed
Catherine
Kim
Kim
Kim
Hazem
Sam
Humberto
Gustavo
Pilar
I want to sort them to:
Catherine
Gustavo
Hazem
Humberto
Kim
Kim
Kim
Pilar
Sam
Syed
This is what I've tried, but failed:
select top 10 [FirstName] from Person.Person order by [FirstName];
and
select * from
(select top 10 [FirstName] from Person.Person) as persons
order by [FirstName];
and
with persons as (select top 10 [FirstName] from Person.Person)
select * from persons order by [FirstName];
When you don't specify an ORDER BY, sql server will return the values in whatever order is convenient, there is no guarantee it'll stay the same on subsequent executions. So a TOP(x) without an ORDER BY is usually senseless, because those x can be any x rows.
If you really want to sort those random 10 rows, you should use a sub query as you did. You can see sql server is free to choose any order it sees fit, because you didn't tell it what you want.
If you really, really want to sort those rows, you can try to insert them into a temporary table or table variable first. But again, I suspect you'll find sql server will decide on 10 different rows.
A nice way to visualize it (sort of) is to look at the execution plan: no ORDER BY means no sort, so the rows are shown in the order that they come in (things get a tad mythical beyond that).
How can I LIMIT the result returned by a query in Adaptive Server IQ/12.5.0/0306?
The following gives me a generic error near LIMIT:
SELECT * FROM mytable LIMIT 10, 10;
Any idea why? This is my first time with this dbms
Sybase IQ uses row_count to limit the number of rows returned.
You will have to set the row count at the beginning of your statement and decide whether the statement should be TEMPORARY or not.
ROW_COUNT
SET options
LIMIT statement is not supported in Sybase IQ 12. I think there is not simple or clean solution, similarly like in old SQL server. But there are some approches that works for SQL server 2000 and should work also for Sybase IQ 12. I don't promise that queries below will work on copy&paste.
Subquery
SELECT TOP 10 *
FROM mytable
WHERE Id NOT IN (
SELECT TOP 10 Id FROM mytable ORDER BY OrderingColumn
)
ORDER BY OrderingColumn
Basically, it fetches 10 rows but also skips first 10 rows. To get this works, rows must be unique and ordering is important. Id cannot be more times in results. Otherwise you can filter out valid rows.
Asc-Desc
Another workaround depends on ordering. It uses ordering and fetches 10 rows for second page and you have to take care of last page (it does not work properly with simple formula page * rows per page).
SELECT *
FROM
(
SELECT TOP 10 *
FROM
(
SELECT TOP 20 * -- (page * rows per page)
FROM mytable
ORDER BY Id
) AS t1
ORDER BY Id DESC
) AS t2
ORDER BY Id ASC
I've found some info about non working subqueries in FROM statement in ASE 12. This approach maybe is not possible.
Basic iteration
In this scenario you can just iterate through rows. Let's assume id of tenth row is 15. Then it will select next 10 rows after tenth row. Bad things happen when you will order by another column than Id. It is not possible.
SELECT TOP 10 *
FROM mytable
WHERE Id > 15
ORDER BY Id
Here is article about another workarounds in SQL server 2000. Some should also works in similar ways in Sybase IQ 12.
http://www.codeproject.com/Articles/6936/Paging-of-Large-Resultsets-in-ASP-NET
All those things are workarounds. If you can try to migrate on newer version.
I have a view that may contain more than one row, looking like this:
[rate] | [vendorID]
8374 1234
6523 4321
5234 9374
In a SPROC, I need to set a param equal to the value of the first column from the first row of the view. something like this:
DECLARE #rate int;
SET #rate = (select top 1 rate from vendor_view where vendorID = 123)
SELECT #rate
But this ALWAYS returns the LAST row of the view.
In fact, if I simply run the subselect by itself, I only get the last row.
With 3 rows in the view, TOP 2 returns the FIRST and THIRD rows in order. With 4 rows, it's returning the top 3 in order. Yet still top 1 is returning the last.
DERP?!?
This works..
DECLARE #rate int;
CREATE TABLE #temp (vRate int)
INSERT INTO #temp (vRate) (select rate from vendor_view where vendorID = 123)
SET #rate = (select top 1 vRate from #temp)
SELECT #rate
DROP TABLE #temp
.. but can someone tell me why the first behaves so fudgely and how to do what I want? As explained in the comments, there is no meaningful column by which I can do an order by. Can I force the order in which rows are inserted to be the order in which they are returned?
[EDIT] I've also noticed that: select top 1 rate from ([view definition select]) also returns the correct values time and again.[/EDIT]
That is by design.
If you don't specify how the query should be sorted, the database is free to return the records in any order that is convenient. There is no natural order for a table that is used as default sort order.
What the order will actually be depends on how the query is planned, so you can't even rely on the same query giving a consistent result over time, as the database will gather statistics about the data and may change how the query is planned based on that.
To get the record that you expect, you simply have to specify how you want them sorted, for example:
select top 1 rate
from vendor_view
where vendorID = 123
order by rate
I ran into this problem on a query that had worked for years. We upgraded SQL Server and all of a sudden, an unordered select top 1 was not returning the final record in a table. We simply added an order by to the select.
My understanding is that SQL Server normally will generally provide you the results based on the clustered index if no order by is provided OR off of whatever index is picked by the engine. But, this is not a guarantee of a certain order.
If you don't have something to order off of, you need to add it. Either add a date inserted column and default it to GETDATE() or add an identity column. It won't help you historically, but it addresses the issue going forward.
While it doesn't necessarily make sense that the results of the query should be consistent, in this particular instance they are so we decided to leave it 'as is'. Ultimately it would be best to add a column, but this was not an option. The application this belongs to is slated to be discontinued sometime soon and the database server will not be upgraded from SQL 2005. I don't necessarily like this outcome, but it is what it is: until it breaks it shall not be fixed. :-x
INTRODUCTION TO DATABASE TABLE BEING USED -
I am working on a “Stock Market Prices” based Database Table. My table has got the data for the following FIELDS –
ID
SYMBOL
OPEN
HIGH
LOW
CLOSE
VOLUME
VOLUME CHANGE
VOLUME CHANGE %
OPEN_INT
SECTOR
TIMESTAMP
New data gets added to the table daily “Monday to Friday”, based on the stock market price changes for that day. The current requirement is based on the VOLUME field, which shows the volume traded for a particular stock on daily basis.
REQUIREMENT –
To get the Average and Total Volume for last 10,15 and 30 Days respectively.
METHOD USED CURRENTLY -
I created these 9 SEPARATE QUERIES in order to get my desired results –
First I have created these 3 queries to take out the most recent last 10,15 and 30 dates from the current table:
qryLast10DaysStored
qryLast15DaysStored
qryLast30DaysStored
Then I have created these 3 queries for getting the respective AVERAGES:
qrySymbolAvgVolume10Days
qrySymbolAvgVolume15Days
qrySymbolAvgVolume30Days
And then I have created these 3 queries for getting the respective TOTALS:
qrySymbolTotalVolume10Days
qrySymbolTotalVolume15Days
qrySymbolTotalVolume30Days
PROBLEM BEING FACED WITH CURRENT METHOD -
Now, my problem is that I have ended up having these so many different queries, whereas I wanted to get the output into One Single Query, as shown in the Snapshot of the Excel Sheet:
http://i49.tinypic.com/256tgcp.png
SOLUTION NEEDED -
Is there some way by which I can get these required fields into ONE SINGLE QUERY, so that I do not have to look into multiple places for the required fields? Can someone please tell me how to get all these separate queries into one -
A) Either by taking out or moving the results from these separate individual queries to one.
B) Or by making a new query which calculates all these fields within itself, so that these separate individual queries are no longer needed. This would be a better solution I think.
One Clarification about Dates –
Some friend might think why I used the method of using Top 10,15 and 30 for getting the last 10,15 and 30 Date Values. Why not I just used the PC Date for getting these values? Or used something like -
("VOLUME","tbl-B", "TimeStamp BETWEEN Date() - 10 AND Date()")
The answer is that I require my query to "Read" the date from the "TIMESTAMP" Field, and then perform its calculations accordingly for LAST / MOST RECENT "10 days, 15 days, 30 days” FOR WHICH THE DATA IS AVAILABLE IN THE TABLE, WITHOUT BOTHERING WHAT THE CURRENT DATE IS. It should not depend upon the current date in any way.
If there is any better method or more efficient way to create these queries, then please enlighten.
You have separate queries to compute 10DayTotalVolume and 10DayAvgVolume. I suspect you can compute both in one query, qry10DayVolumes.
SELECT
b.SYMBOL,
Sum(b.VOLUME) AS 10DayTotalVolume,
Avg(b.VOLUME) AS 10DayAvgVolume
FROM
[tbl-B] AS b INNER JOIN
qryLast10DaysStored AS q
ON b.TIMESTAMP = q.TIMESTAMP
GROUP BY b.SYMBOL;
However, that makes me wonder whether 10DayAvgVolume can ever be anything other than 10DayTotalVolume / 10
Similar considerations apply to the 15 and 30 day values.
Ultimately, I think you want something based on a starting point like this:
SELECT
q10.SYMBOL,
q10.[10DayTotalVolume],
q10.[10DayAvgVolume],
q15.[15DayTotalVolume],
q15.[15DayAvgVolume],
q30.[30DayTotalVolume],
q30.[30DayAvgVolume]
FROM
(qry10DayVolumes AS q10
INNER JOIN qry15DayVolumes AS q15
ON q10.SYMBOL = q15.SYMBOL)
INNER JOIN qry30DayVolumes AS q30
ON q10.SYMBOL = q30.SYMBOL;
That assumes you have created qry15DayVolumes and qry30DayVolumes following the approach I suggested for qry10DayVolumes.
If you want to cut down the number of queries, you could use subqueries for each of the qry??DayVolumes saved queries, but try it this way first to make sure the logic is correct.
In that second query above, there can be a problem due to field names which start with digits. Enclose those names in square brackets or re-alias them in qry10DayVolumes, qry15DayVolumes, and qry30DayVolumes using alias names which begin with letters instead of digits.
I tested the query as written above with the "2nd Upload.mdb" you uploaded, and it ran without error from Access 2007. Here is the first row of the result set from that query:
SYMBOL 10DayTotalVolume 10DayAvgVolume 15DayTotalVolume 15DayAvgVolume 30DayTotalVolume 30DayAvgVolume
ACC-1 42909 4290.9 54892 3659.46666666667 89669 2988.96666666667
Access doesn't support most advanced SQL syntax and clauses, so this is a bit of a hack, but it works, and is fast on your small sample. You're basically running 3 queries but the Union clauses allow you to combine into one:
select
Symbol,
sum([10DayTotalVol]) as 10DayTotalV,
sum([10DayAvgVol]) as 10DayAvgV,
sum([15DayTotalVol]) as 15DayTotalV,
sum([15DayAvgVol]) as 15DayAvgV,
sum([30DayTotalVol]) as 30DayTotalV,
sum([30DayAvgVol]) as 30DayAvgV
from (
select
Symbol,
sum(volume) as 10DayTotalVol, avg(volume) as 10DayAvgVol,
0 as 15DayTotalVol, 0 as 15DayAvgVol,
0 as 30DayTotalVol, 0 as 30DayAvgVol
from
[tbl-b]
where
timestamp >= (select min(ts) from (select distinct top 10 timestamp as ts from [tbl-b] order by timestamp desc ))
group by
Symbol
UNION
select
Symbol,
0, 0,
sum(volume), avg(volume),
0, 0
from
[tbl-b]
where
timestamp >= (select min(ts) from (select distinct top 15 timestamp as ts from [tbl-b] order by timestamp desc ))
group by
Symbol
UNION
select
Symbol,
0, 0,
0, 0,
sum(volume), avg(volume)
from
[tbl-b]
where
timestamp >= (select min(ts) from (select distinct top 30 timestamp as ts from [tbl-b] order by timestamp desc ))
group by
Symbol
) s
group by
Symbol
Is there a way in MS access to return a dataset between a specific index?
So lets say my dataset is:
rank | first_name | age
1 Max 23
2 Bob 40
3 Sid 25
4 Billy 18
5 Sally 19
But I only want to return those records between 'rank' 2 and 4, so my results set is Bob, Sid and Billy? However, Rank is not part of the table, and this should be generated when the query is run. Why don't I use an autogenerated number, because if a record is deleted, this will be inconsistent, and what if I wanted the results in reverse!
This obviously very simple, and the reason I ask is because I am working on a product catalogue and I am looking for a more efficient way of paging through the returned dataset, so if I only return 1 page worth of data from the database this is obviously going to be quicker then return a complete set of 3000 records and then having to subselect from that set!
Thanks R.
Original suggestion:
SELECT * from table where rank BETWEEN 2 and 4;
Modified after comment, that rank is not existing in structure:
Select top 100 * from table;
And if you want to choose subsequent results, you can choose the ID of the last record from the first query, say it was ID 101, and use a WHERE clause to get the next 100;
Select top 100 * from table where ID > 100;
But these won't give you what you're looking for either, I bet.
How are you calculating rank? I assume you are basing it on some data in another dataset somewhere. If so, create a function, do a table join, or do something that can calculate rank based on values in other table(s), then you can do queries based on the rank() function.
For example:
select *
from table
where rank() between 2 and 4
If you are not calculating rank based on some data somewhere, there really isn't a way to write this query, and you might as well be returning three random rows from the table.
I think you need to use a correlated subquery to calculate the rank on the fly e.g. I'm guessing the rank is based on name:
SELECT T1.first_name, T1.age,
(
SELECT COUNT(*) + 1
FROM MyTable AS T2
WHERE T1.first_name > T2.first_name
) AS rank
FROM MyTable AS T1;
The bad news is the Access data engine is poorly optimized for this kind of query; in my experience, performace will start to noticeably degrade beyond a few hundred rows.
If it is not possible to maintain the rank on the db side of the house (e.g. high insertion environment) consider doing the paging on the client side. For example, an ADO classic recordset object has properties to support paging (PageCount, PageSize, AbsolutePage, etc), something for which DAO recordsets (being of an older vintage) have no support.
As always, you'll have to perform your own timings but I suspect that when there are, say, 10K rows you will find it faster to take on the overhead of fetching all the rows to an ADO recordset then finding the page (then perhaps fabricate smaller ADO recordset consisting of just that page's worth of rows) than it is to perform a correlated subquery to only fetch the number of rows for the page.
Unfortunately the LIMIT keyword isn't available in MS Access -- that's what is used in MySQL for a multi-page presentation. If you can write an order key into the results table, then you can use it something like this:
SELECT TOP 25 MyOrder, Etc FROM Table1 WHERE MyOrder in
(SELECT TOP 55 MyOrder FROM Table1 ORDER BY MyOrder DESC)
ORDER BY MyOrder ASCENDING
If I understand you correctly, there is ionly first_name and age columns in your table. If this is the case, then there is no way to return Bob, Sid, and Billy with a single query. Unless you do something like
SELECT * FROM Table
WHERE FirstName = 'Bob'
OR FirstName = 'Sid'
OR FirstName = 'Billy'
But I think that this is not what you are looking for.
This is because SQL databases make no guarantee as to the order that the data will come out of the database unless you specify an ORDER BY clause. It will usually come out in the same order it was added, but there are no guarantees, and once you get a lot of rows in your table, there's a reasonably high probability that they won't come out in the order you put them in.
As a side note, you should probably add a "rank" column (this column is usually called id) to your table, and make it an auto incrementing integer (see Access documentation), so that you can do the query mentioned by Sev. It's also important to have a primary key so that you can be certain which rows are being updated when you are running an update query, or which rows are being deleted when you run a delete query. For example, if you had 2 people named Max, and they were both 23, how you delete 1 row without deleting the other. If you had another auto incrementing unique column in there, you could specify the unique ID in your query to delete only one.
[ADDITION]
Upon reading your comment, If you add an autoincrement field, and want to read 3 rows, and you know the ID of the first row you want to read, then you can use "TOP" to read 3 rows.
Assuming your data looks like this
ID | first_name | age
1 Max 23
2 Bob 40
6 Sid 25
8 Billy 18
15 Sally 19
You can wuery Bob, Sid and Billy with the following QUERY.
SELECT TOP 3 FirstName, Age
From Table
WHERE ID >= 2
ORDER BY ID