I have a table that has an auto-incrementing identity "Reference" field and a pair of other fields that determine the sort order. What I need to do is find the 'next' item in the table when sorted based on the pair of fields based on the reference field of an initial item.
So my data looks like this when sorted by SortParent.SortChild:
Reference SortParent SortChild Data
------------------------------------------
9 1 2 Fred
7 1 3 Jim
11 1 4 Sheila
4 2 1 Micro
5 2 2 Archimedes
12 2 3 Electron
So in this example the "Jim" row (Reference=7) comes after "Fred" (Reference=9) even though it's reference is smaller.
So i want to be able to find which row comes after Fred by searching based on Jim's reference
At the moment in code I do a query to find the values for Fred's row:
SELECT SortParent,SortChild From MyTable WHERE Reference=9
Which returns 1,2. Then do a search for the first row that comes after 1,2:
SELECT * FROM MyTable
WHERE ((SortParent=1 and SortChild>2) OR (SortParent>2))
ORDER BY SortParent,SortChild
Which will therefore come back with the row having reference 7 and sort values 1,3
I'm pretty sure this can be done in a single query, but i'm stumped on the best way.
Incidentally, if anyone has any suggestions on alternate way of handling the two part sort columns that would make this easier, please feel free to help!
I believe You are looking at the LEAD or LAG windowed function:
https://msdn.microsoft.com/en-US/library/hh213125.aspx
SELECT
NextReference
FROM
(SELECT
reference
, LEAD(reference, 1,0) OVER (ORDER BY SortParent,SortChild) AS NextReference
, *
FROM
mytable
) newTable
WHERE
reference = 9
I used LEAD, but try it with LAG if you are looking in the other direction for the row
I havn't tested this particular query, so my not be syntactically sound, but let me know if you have any troubles with it and I'll go over it a bit more once I'm back at my desk
EDIT: Used the wrong sql from your question as my base
EDIT2: Put the lead into a subquery to allow us to query on it
Related
I accepted a new feature to re-order some items by using Drag-and-Drop UI and save the preference for each user to the database. What's the best way to do so?
After reading some questions on StackOverflow, I found this solution.
Solution 1: Use decimal numbers to indicate order
For example,
id item order
1 a 1
2 b 2
3 c 3
4 d 4
If I insert item 4 between item 1 and 2, the order becomes,
id item order
1 a 1
4 d 1.5
2 b 2
3 c 3
In this way, every new order = order[i-1] + order[i+1] / 2
If I need to save the preference for every user, then I need to another relationship table like this,
user_id item_id order
1 1 1
1 2 2
1 3 3
1 4 1.5
I need num_of_users * num_of_items records to save this preference.
However, there's a solution I can think of.
Solution 2: Save the order preference in a column in the User table
This is straightforward by adding a column in the User table to record the order. Each value would be parsed as an array of item_ids that ranked by the index of the array.
user_id . item_order
1 [1,4,2,3]
2 [1,2,3,4]
Is there any limitation of this solution? Or is there any other ways to solve this problem?
Usually, an explicit ordering deals with the presentation or some specific processing of data. Hence, it's a good idea to separate entities of theirs presentation/processing. For example
users
-----
user_id (PK)
user_login
...
user_lists
----------
list_id, user_id (PK)
item_index
item_index can be a simply integer value :
ordered continuously (1,2...N): DELETE/INSERT of the whole list are normally required to change the order
ordered discretely with some seed (10,20...N): you can insert new items without reordering the whole list
Another reason to separate entity data and lists: reordering lists should be done in transaction that may lead to row/table locks. In case of separated tables only data in list table is impacted.
Ok, from the title it seems to be impossible to understand, I'll try to be as clear as possible.
Basically, I have a table, let's call it 'records'. In this table I have some products, of which I store 'id', 'codex' (which is a unique identifier for a certain product in the whole database), 'price' and 'situation'. This last one is a string which tells me wether the product has just entered the store (in that case it is set to 'IN'), or it has already been sold ('OUT' in this case).
The database was not created by us, I HAVE to work with that although it is horribly structured... The guy who originally projected the database decided to register when a product's situation passes from 'IN' to 'OUT' in the following way: instead of UPDATEing the corresponding value in the table, he used to take the row of data with 'IN' as situation, and to DUPLICATE it setting, that time, 'OUT' as situation.
Just to sum up: if a product has not been sold yet, it will have one row of dedicated data; otherwise those rows will be two, identical except for the 'situation' field.
What I need to do is: select a product if (and ONLY if) there is no duplicate for it. Basically, I can (and should) look for a 'codex', and if I my Count(codex) ends up being >1, I do not select the row.
I hope the explanation of the process is clear enough...
I tryed many alternative (no, SELECT DISTINCT is not a solution): des anyone have an idea of how to do that? Because really, none of us three could come up with a good solution!
Here is the schema for the table, I hope it is sufficiently clear, and if not do not hesitate asking for more details.
Just as a reminder: the project is in (sigh...) VB.net, the database is in Microsoft Access (mdb).
I could not find a solution on StackOverFlow, I hope this is not a duplicate question! Thanks in advance for the help.
id codex price situation
1 1 2.50 IN
2 1 2.50 OUT
3 2 3.45 IN
4 3 21.50 IN
5 2 3.45 OUT
6 4 1.50 IN
To check if I understand what your problem is... In your example table you just want to get the lines with ID 4 a 6, right?
If is that what you want, and If you want only the not sold ones try this command
SELECT
*
FROM
records
WHERE
codex
not in
(
SELECT
codex
FROM
records
WHERE
situation ='OUT'
)
I have a indexed table where one of the indexed columns can contains data with an underscore.
ID Name
1 01_A3L
2 02_A3L
3 03_A3L
4 05_A3L
5 some name
6 another name
7 a name
When I search this table with the following query however I don't get any results:
SELECT * FROM MyAmazingTable WHERE( CONTAINS(*,'"a3l*"'))
What is the reason for this? And how can I make sure I do get results I expect (all records that end with A3L)?
Kees C Bakker is 100% correct, but if you just wanted to get the results you require without all of the steps.
The quick/dirty way to do so would be change your search to be a like...
Select * from MyAmazingTable where Name like '%A3L'
The % in this case would represent whatever comes before and make sure the last 3 characters are A3L.
Which will give you the results that you are looking for.
Let's say I have a Product table in a shopping site's database to keep description, price, etc of store's products. What is the most efficient way to make my client able to re-order these products?
I create an Order column (integer) to use for sorting records but that gives me some headaches regarding performance due to the primitive methods I use to change the order of every record after the one I actually need to change. An example:
Id Order
5 3
8 1
26 2
32 5
120 4
Now what can I do to change the order of the record with ID=26 to 3?
What I did was creating a procedure which checks whether there is a record in the target order (3) and updates the order of the row (ID=26) if not. If there is a record in target order the procedure executes itself sending that row's ID with target order + 1 as parameters.
That causes to update every single record after the one I want to change to make room:
Id Order
5 4
8 1
26 3
32 6
120 5
So what would a smarter person do?
I use SQL Server 2008 R2.
Edit:
I need the order column of an item to be enough for sorting with no secondary keys involved. Order column alone must specify a unique place for its record.
In addition to all, I wonder if I can implement something like of a linked list: A 'Next' column instead of an 'Order' column to keep the next items ID. But I have no idea how to write the query that retrieves the records with correct order. If anyone has an idea about this approach as well, please share.
Update product set order = order+1 where order >= #value changed
Though over time you'll get larger and larger "spaces" in your order but it will still "sort"
This will add 1 to the value being changed and every value after it in one statement, but the above statement is still true. larger and larger "spaces" will form in your order possibly getting to the point of exceeding an INT value.
Alternate solution given desire for no spaces:
Imagine a procedure for: UpdateSortOrder with parameters of #NewOrderVal, #IDToChange,#OriginalOrderVal
Two step process depending if new/old order is moving up or down the sort.
If #NewOrderVal < #OriginalOrderVal --Moving down chain
--Create space for the movement; no point in changing the original
Update product set order = order+1
where order BETWEEN #NewOrderVal and #OriginalOrderVal-1;
end if
If #NewOrderVal > #OriginalOrderVal --Moving up chain
--Create space for the momvement; no point in changing the original
Update product set order = order-1
where order between #OriginalOrderVal+1 and #NewOrderVal
end if
--Finally update the one we moved to correct value
update product set order = #newOrderVal where ID=#IDToChange;
Regarding best practice; most environments I've been in typically want something grouped by category and sorted alphabetically or based on "popularity on sale" thus negating the need to provide a user defined sort.
Use the old trick that BASIC programs (amongst other places) used: jump the numbers in the order column by 10 or some other convenient increment. You can then insert a single row (indeed, up to 9 rows, if you're lucky) between two existing numbers (that are 10 apart). Or you can move row 370 to 565 without having to change any of the rows from 570 upwards.
Here is an alternative approach using a common table expression (CTE).
This approach respects a unique index on the SortOrder column, and will close any gaps in the sort order sequence that may have been left over from earlier DELETE operations.
/* For example, move Product with id = 26 into position 3 */
DECLARE #id int = 26
DECLARE #sortOrder int = 3
;WITH Sorted AS (
SELECT Id,
ROW_NUMBER() OVER (ORDER BY SortOrder) AS RowNumber
FROM Product
WHERE Id <> #id
)
UPDATE p
SET p.SortOrder =
(CASE
WHEN p.Id = #id THEN #sortOrder
WHEN s.RowNumber >= #sortOrder THEN s.RowNumber + 1
ELSE s.RowNumber
END)
FROM Product p
LEFT JOIN Sorted s ON p.Id = s.Id
It is very simple. You need to have "cardinality hole".
Structure: you need to have 2 columns:
pk = 32bit int
order = 64bit bigint (BIGINT, NOT DOUBLE!!!)
Insert/UpdateL
When you insert first new record you must set order = round(max_bigint / 2).
If you insert at the beginning of the table, you must set order = round("order of first record" / 2)
If you insert at the end of the table, you must set order = round("max_bigint - order of last record" / 2)
If you insert in the middle, you must set order = round("order of record before - order of record after" / 2)
This method has a very big cardinality. If you have constraint error or if you think what you have small cardinality you can rebuild order column (normalize).
In maximality situation with normalization (with this structure) you can have "cardinality hole" in 32 bit.
It is very simple and fast!
Remember NO DOUBLE!!! Only INT - order is precision value!
One solution I have used in the past, with some success, is to use a 'weight' instead of 'order'. Weight being the obvious, the heavier an item (ie: the lower the number) sinks to the bottom, the lighter (higher the number) rises to the top.
In the event I have multiple items with the same weight, I assume they are of the same importance and I order them alphabetically.
This means your SQL will look something like this:
ORDER BY 'weight', 'itemName'
hope that helps.
I am currently developing a database with a tree structure that needs to be ordered. I use a link-list kind of method that will be ordered on the client (not the database). Ordering could also be done in the database via a recursive query, but that is not necessary for this project.
I made this document that describes how we are going to implement storage of the sort order, including an example in postgresql. Please feel free to comment!
https://docs.google.com/document/d/14WuVyGk6ffYyrTzuypY38aIXZIs8H-HbA81st-syFFI/edit?usp=sharing
i have three tables
documents
attributes
attributevalues
documents can have many attributes
and these atributes have value in attributevalue table
what i want in single query get all documents and assigned atributes of relevant documents in row each row
(i assume every documents have same attributes assigned dont need complexity of diffrent attribues now)
for example
docid attvalue1 attvalue2
1 2 2
2 2 2
3 1 1
how can i do that in single query
Off the top if my head, I don't think you can do this without dynamic SQL.
The crux of the Entity-Attribute-Value (EAV) technique (which is what you are using) is to store columns as rows. What you want to do is convert those rows back to columns for the purpose of this query. Using PIVOT makes this possible. However, PIVOT requires knowing the number of rows that need to be converted to columns at the time the query is written. So assuming you are using EAV because you need flexible attributes/values, you won't know this information when you write the query.
So the solution would be to use dynamic SQL in conjunction with PIVOT. Did a quick search and this looks promising (didn't really read the whole thing):
http://www.simple-talk.com/community/blogs/andras/archive/2007/09/14/37265.aspx
For the record, I am not a fan of dynamic SQL and would recommend finding another approach to the larger problem (e.g. pivoting in application code).
If you know all the attributes (and their IDs) at design-time:
SELECT d.docid,
a1.attvalue AS attvalue1
a2.attvalue AS attvalue2
FROM documents d
JOIN attributevalues a1 ON d.docid = a1.docid
JOIN attributevalues a2 ON d.docid = a2.docid
WHERE a1.attrid = 1
AND a2.attrid = 2
If you don't, things get quite a bit messier and difficult to answer without knowing your schema.
lets make example
documents table's columns
docid,docname,createddate,createduser
and values
1 account.doc 10.10.2010 aeon
2 hr.doc 10.11.2010 aeon
atributes table's columns
attid,name,type
and values
1 subject string
2 recursive int
attributevalues table's columns
attvalueid,docid,attid,attvalue(sql_variant)
and values
1 1 1 "accounting doc"
1 1 2 0
1 2 1 "humen r doc"
1 2 2 1
and I want query result
docid,name,atribvalue1,atribvalue1,atribvalueN
1 account.doc "accounting doc" 0
2 hr.doc "humen r doc" 1