I have this code
var items = query.Skip(0).Take(25).List();
what I want is that I get 25 entrance from my list(list got 402 entrance).
I never got 25 entrance after this call. Does someone know why?
A .Take() and .Skip() is at DB side (e.g. on SQL Server - Implement paging (skip / take) functionality with this query) converted into something like this
SELECT col1, col2, ...
FROM ...
WHERE ...
ORDER BY
OFFSET 0 ROWS -- skip 0 rows
FETCH NEXT 25 ROWS ONLY; -- take 25 rows
And that would always work if our query is about one TABLE (no JOIN). I.e. that many rows will result in that many C# items in the result list
But if a query would use JOIN, joining some collection, we would still get 25 rows on DB side..
parent_id, child_id
1, 10
1, 11
2, 12
2, 13
...
-- 25 rows
But these would result in less root entities (see parent 1 and 2 has 4 rows). These will, during transformation, be simply converted in just few parents with very uncertain amount of items in collection
My suggestion would be:
do not join collection when paging is needed. NEVER. Always page on joins related to star schema (many-to-one)
Related
I have two tables. I want to find the erroneous records in the first table based on the fact that they aren't complete set as determined by the second table. eg:
custID service transID
1 20 1
1 20 2
1 50 2
2 49 1
2 138 1
3 80 1
3 140 1
comboID combinations
1 Y00020Y00050
2 Y00049Y00138
3 Y00020Y00049
4 Y00020Y00080Y00140
So in this example I would want a query to return the first row of the first table because it does not have a matching 49 or 50 or (80 and 140), and the last two rows as well (because there is no 20). The second transaction is fine, and the second customer is fine.
I couldn't figure this out with a query, so I wound up writing a program that loads the services per customer and transid into an array, iterates over them, and ensures that there is at least one matching combination record where all the services in the combination are present in the initially loaded array. Even that came off as hamfisted, but it was less of a nightmare than the awkward outer joining of multiple joins I was trying to accomplish with SQL.
Taking a step back, I think I need to restructure the combinations table into something more accommodating, but I still can't think of what the approach would be.
I do not have DB2 so I have tested on Oracle. However listagg function should be there as well. The table service is the first table and comb the second one. I assume the service numbers to be sorted as in the combinations column.
select service.*
from service
join
(
select S.custid, S.transid
from
(
select custid, transid, listagg(concat('Y000',service)) within group(order by service) as agg
from service
group by custid, transid
) S
where not exists
(
select *
from comb
where S.agg = comb.combinations
)
) NOT_F on NOT_F.custid = service.custid and NOT_F.transid = service.transid
I dare to say that your database design does not conform to the first normal form since the combinations column is not atomic. Think about it.
What I am trying to do is fairly simple. I just want to add a row number to a query. Since this is in Access is a bit more difficult than other SQL, but under normal circumstances is still doable using solutions such as DCount or Select Count(*), example here: How to show row number in Access query like ROW_NUMBER in SQL or Access SQL how to make an increment in SELECT query
My Issue
My issue is I'm trying to add this counter to a multi-join query that orders by fields from numerous tables.
Troubleshooting
My code is a bit ridiculous (19 fields, seven of which are long expressions, from 9 different joined tables, and ordered by fields from 5 of those tables). To make things simple, I have an simplified example query below:
Example Query
SELECT DCount("*","Requests_T","[Requests_T].[RequestID]<=" & [Requests_T].[RequestID]) AS counter, Requests_T.RequestHardDeadline AS Deadline, Requests_T.RequestOverridePriority AS Priority, Requests_T.RequestUserGroup AS [User Group], Requests_T.RequestNbrUsers AS [Nbr of Users], Requests_T.RequestSubmissionDate AS [Submitted on], Requests_T.RequestID
FROM (((((((Requests_T
INNER JOIN ENUM_UserGroups_T ON ENUM_UserGroups_T.UserGroups = Requests_T.RequestUserGroup)
INNER JOIN ENUM_RequestNbrUsers_T ON ENUM_RequestNbrUsers_T.NbrUsers = Requests_T.RequestNbrUsers)
INNER JOIN ENUM_RequestPriority_T ON ENUM_RequestPriority_T.Priority = Requests_T.RequestOverridePriority)
ORDER BY Requests_T.RequestHardDeadline, ENUM_RequestPriority_T.DisplayOrder DESC , ENUM_UserGroups_T.DisplayOrder, ENUM_RequestNbrUsers_T.DisplayOrder DESC , Requests_T.RequestSubmissionDate;
If the code above is trying to select a field from a table not included, I apologize - just trust the field comes from somewhere (lol i.e. one of the other joins I excluded to simply the query). A great example of this is the .DisplayOrder fields used in the ORDER BY expression. These are fields from a table that simply determines the "priority" of an enum. Example: Requests_T.RequestOverridePriority displays to the user as an combobox option of "Low", "Med", "High". So in a table, I assign a numerical priority to these of "1", "2", and "3" to these options, respectively. Thus when ENUM_RequestPriority_T.DisplayOrder DESC is called in order by, all "High" priority requests will display above "Medium" and "Low". Same holds true for ENUM_UserGroups_T.DisplayOrder and ENUM_RequestNbrUsers_T.DisplayOrder.
I'd also prefer to NOT use DCOUNT due to efficiency, and rather do something like:
select count(*) from Requests_T where Requests_T.RequestID>=RequestID) as counter
Due to the "Order By" expression however, my 'counter' doesn't actually count my resulting rows sequentially since both of my examples are tied to the RequestID.
Example Results
Based on my actual query results, I've made an example result of the query above.
Counter Deadline Priority User_Group Nbr_of_Users Submitted_on RequestID
5 12/01/2016 High IT 2-4 01/01/2016 5
7 01/01/2017 Low IT 2-4 05/06/2016 8
10 Med IT 2-4 07/13/2016 11
15 Low IT 10+ 01/01/2016 16
8 Low IT 2-4 01/01/2016 9
2 Low IT 2-4 05/05/2016 2
The query is displaying my results in the proper order (those with the nearest deadline at the top, then those with the highest priority, then user group, then # of users, and finally, if all else is equal, it is sorted by submission date). However, my "Counter" values are completely wrong! The counter field should simply intriment +1 for each new row. Thus if displaying a single request on a form for a user, I could say
"You are number: Counter [associated to RequestID] in the
development queue."
Meanwhile my results:
Aren't sequential (notice the first four display sequentially, but then the final two rows don't)! Even though the final two rows are lower in priority than the records above them, they ended up with a lower Counter value simply because they had the lower RequestID.
They don't start at "1" and increment +1 for each new record.
Ideal Results
Thus my ideal result from above would be:
Counter Deadline Priority User_Group Nbr_of_Users Submitted_on RequestID
1 12/01/2016 High IT 2-4 01/01/2016 5
2 01/01/2017 Low IT 2-4 05/06/2016 8
3 Med IT 2-4 07/13/2016 11
4 Low IT 10+ 01/01/2016 16
5 Low IT 2-4 01/01/2016 9
6 Low IT 2-4 05/05/2016 2
I'm spoiled by PLSQL and other software where this would be automatic lol. This is driving me crazy! Any help would be greatly appreciated.
FYI - I'd prefer an SQL option over VBA if possible. VBA is very much welcomed and will definitely get an up vote and my huge thanks if it works, but I'd like to mark an SQL option as the answer.
Unfortuantely, MS Access doesn't have the very useful ROW_NUMBER() function like other clients do. So we are left to improvise.
Because your query is so complicated and MS Access does not support common table expressions, I recommend you follow a two step process. First, name that query you already wrote IntermediateQuery. Then, write a second query called FinalQuery that does the following:
SELECT i1.field_primarykey, i1.field2, ... , i1.field_x,
(SELECT field_primarykey FROM IntermediateQuery i2
WHERE t2.field_primarykey <= t1.field_primarykey) AS Counter
FROM IntermediateQuery i1
ORDER BY Counter
The unfortunate side effect of this is the more data your table returns, the longer it will take for the inline subquery to calculate. However, this is the only way you'll get your row numbers. It does depend on having a primary key in the table. In this particular case, it doesn't have to be an explicitly defined primary key, it just needs to be a field or combination of fields that is completely unique for each record.
I am currently using Sql Server 2014 Professional and the current version is (12.0.4100). I have a View and I am trying to SELECT 10 rows with specific offset.My View is like below:
BeginTime | EndTime | Duration | Name
09:00:00.0000000|16:00:00.0000000| 1 | some_name1
09:00:00.0000000|16:00:00.0000000| 2 | some_name2
09:00:00.0000000|16:00:00.0000000| 3 | some_name3
09:00:00.0000000|16:00:00.0000000| 4 | some_name4
09:00:00.0000000|16:00:00.0000000| 5 | some_name5
09:00:00.0000000|16:00:00.0000000| 6 | some_name6
09:00:00.0000000|16:00:00.0000000| 7 | some_name7
there are 100 rows like these and all have the exact same value in BeginTime and EndTime. Duration is incremented from 1 to 100 in related table. If query is only:
SELECT * FROM View_Name
ResultSet is correct. I can understand it by checking the duration column.
If I want to fetch only 10 rows starting from 0, ResultSet is correct and it is correct for starting from up to 18. When I want to fetch 10 rows starting from 19 or more than 19, Duration in ResultSet returns irrelevant results like Duration reversed. But it never returns the rows which has duration more than 11.
The query that I used to fetch specific rows is as follows:
SELECT * FROM View_Name ORDER BY BeginTime ASC OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY
There is also something strange in this situation; if I specify USE master, this problem disappears, but, if I specify USE [mydb_name], the problem appears again. By the way, I am using SQL SERVER 2014 Professional v(12.0.2269) in my local pc, this problem disappears for the above situation.
PS: I can not use USE master because, I am creating and listing the view dynamically, in Stored Procedures. Any help, answer or comment will be accepted. Thank You!
The documentation explains:
To achieve stable results between query requests using OFFSET and
FETCH, the following conditions must be met:
. . .
The ORDER BY clause contains a column or combination of columns that are guaranteed to be unique.
What happens in your case is that BeginTime is not unique. Databases in general -- and SQL Server in particular -- do not implement stable sorts. A stable sort is one where the rows are in the same order when the keys are the same. This is rather obvious, because tables and result sets represent unordered sets. They have no inherent ordering.
So, you need a unique key to make the sort stable. Given your data, this would seem to be either duration, name, or both:
SELECT *
ROM View_Name
ORDER BY BeginTime ASC, Duration, Name
OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY;
your order by should be unique,otherwise you will get indeterministic results(in your case ,begin time is not unique and your are not guarnteed to get same results every time).try changing your query to below to make it unique..
SELECT * FROM View_Name ORDER BY duration OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY
Further to add ,your first query (select * from view) result set is not guaranteed to be accurate every time unless you have an outer order by .
I'm trying to create a query that will insert new records to a table or update already existing records, but I'm getting stuck on the filtering and grouping for the criteria I want.
I have two tables: tbl_PartInfo, and dbo_CUST_BOOK_LINE.
I'm want to select from dbo_CUST_BOOK_LINE based upon the combination of CUST_ORDER_ID, CUST_ORDER_LINE_NO, and REVISION_ID. Each customer order can have multiple lines, and each line can have multiple revision. I'm trying to select the unique combinations of each order and it's connected lines, but take the connected information for the row with the highest value in the revision column.
I want to insert/update from dbo_CUST_BOOK_LINE the following columns:
CUST_ORDER_ID
PART_ID
USER_ORDER_QTY
UNIT_PRICE
I want to insert/update them into tbl_PartInfo as the following columns respectively:
JobID
DrawingNumber
Quantity
UnitPrice
So if I have the following rows in dbo_CUST_BOOK_LINE (PART_ID omitted for example)
CUST_ORDER_ID CUST_ORDER_LINE_NO REVISION_ID USER_ORDER_QTY UNIT_PRICE
SCabc 1 1 0 100
SCabc 1 2 4 150
SCabc 1 3 4 125
SCabc 2 3 2 200
SCxyz 1 1 0 0
SCxyz 1 2 3 50
It would return
CUST_ORDER_ID CUST_ORDER_LINE_NO (REVISION_ID) USER_ORDER_QTY UNIT_PRICE
SCabc 1 3 4 125
SCabc 2 3 2 200
SCxyz 1 2 3 50
but with PART_ID included and without REVISION_ID
So far, my code is just for the inset portion as I was trying to get the correct records selected, but I keep getting duplicates of CUST_ORDER_ID and CUST_ORDER_LINE_NO.
INSERT INTO tbl_PartInfo ( JobID, DrawingNumber, Quantity, UnitPrice, ProductFamily, ProductCategory )
SELECT dbo_CUST_BOOK_LINE.CUST_ORDER_ID, dbo_CUST_BOOK_LINE.PART_ID, dbo_CUST_BOOK_LINE.USER_ORDER_QTY, dbo_CUST_BOOK_LINE.UNIT_PRICE, dbo_CUST_BOOK_LINE.CUST_ORDER_LINE_NO, Max(dbo_CUST_BOOK_LINE.REVISION_ID) AS MaxOfREVISION_ID
FROM dbo_CUST_BOOK_LINE, tbl_PartInfo
GROUP BY dbo_CUST_BOOK_LINE.CUST_ORDER_ID, dbo_CUST_BOOK_LINE.PART_ID, dbo_CUST_BOOK_LINE.USER_ORDER_QTY, dbo_CUST_BOOK_LINE.UNIT_PRICE, dbo_CUST_BOOK_LINE.CUST_ORDER_LINE_NO;
This has been far more complicated that anything I've done so far, so any help would be greatly appreciated. Sorry about the long column names, I didn't get to choose them.
I did some research and think I found a way to make it work, but I'm still testing it. Right now I'm using three queries, but it should be easily simplified into two when complete.
The first is an append query that takes the two columns I want to get distinct combo's from and selects them and using "group by," while also selecting max of the revision column. It appends them to another table that I'm using called tbl_TempDrop. This table is only being used right now to reduce the number of results before the next part.
The second is an update query that updates tbl_TempDrop to include all the other columns I wanted by setting the criteria equal to the three selected columns from the first query. This took an EXTREMELY long time to complete when I had 700,000 records to work with, hence the use of the tbl_TempDrop.
The third query is a basic append query that appends the rows of tbl_TempDrop to the end destination, tbl_PartInfo.
All that's left is to run all three in a row.
I didn't want to include the full details of any tables or queries yet until I ensure that it works as desired, and because some of the names are vague since I will be using this method for multiple query searches.
This website helped me a little to make sure I had the basic idea down. http://www.techonthenet.com/access/queries/max_query2_2007.php
Let me know if you see any flaws with the ideology!
I have a requirement wherein i need to find the record number of the records that are returned from the resultset. I know that i can use ROWNUM to get the record number from the resultset but my issue is slightly different. below are the details
Table : ProcessSummary
Columns:
PS_PK ProcessId StepId AsscoiateId ProcessName AssetAmount
145 25 50 Process1 3,500.00
267 26 45 Process2 4,400.00
356 27 70 Process3 2,400.00
456 28 80 90 Process4 780.00
556 29 56 67 Process5 4,500.00
656 45 70 Process6 6,000.00
789 31 75 Process7 8,000.00
Now what i need to do is fetch all the records from the ProcessSummary Table when either of ProcessId OR StepId OR AssociateId is NULL. I wrote the below query
select * from ProcessSummary where ProcessId IS NULL OR StepId IS NULL OR AsscoiateId IS NULL
As expected i got 1st, 2nd, 3rd, 6th and 7th records in the resultset that got returned.
Now what i need is to get the records numbers 1,2,3,6,7. I tried to use the ROWNUM as below but i got the values of 1,2,3,4,5 and not 1,2,3,6,7.
select ROWNUM from ProcessSummary where ProcessId IS NULL OR StepId IS NULL OR AsscoiateId IS NULL
Is it possible to get the ROWNUM values in the sequence that i want and if yes then can you please let me know how can i do this. Also if ROWNUM cannot be used then what would be the other option that i can use to get the result in the form that i want.
Any help would be greately appericiated as i could not find much on the net or SO regarding this sort of requirement.
Thanks
Vikeng21
rownum is an internal numbering that gives you a row number based on the current query results only, so that numbering is not tied to a specific record, and it will change when you change the data or the query.
But the numbering you ask for is already in your table. It looks like you just need to SELECT PS_PK .. instead. PS_PK is the field in your table that contains the actual number you want.
You can generate a numbering using an analytical function, and then filter that query. You need some fields to order by, though. In this case I've chosen PS_PK, but it can be another field, like ProcessName or a combination of other fields as well.
select
*
from
(select
dense_rank() over (order by PS_PK) as RANKING,
p.*
from
ProcessSummary p)
where
ProcessId IS NULL OR StepId IS NULL OR AsscoiateId IS NULL
So, in this query, first a numbering is calculated for each row that is returned from the inner query. The numbering is returned as the field RANKING. And then the other query filters further, but still will return the field RANKING with the original numbering.
Instead of dense_rank there is also rank and row_number. The differences are subtle, but you can just experiment and read some docs here and here to learn about the differences and see which one fits you best.
Note that this might slow down your query, because the inner query first generates a number for each row in the table (there is no filtering on that level now).