For background purposes: I'm using PostgreSQL with SQLAlchemy (Python).
Given a table of unique references as such:
references_table
-----------------------
id | reference_code
-----------------------
1 | CODEABCD1
2 | CODEABCD2
3 | CODEWXYZ9
4 | CODEPOIU0
...
In a typical scenario, I would have a separate items table:
items_table
-----------------------
id | item_descr
-----------------------
1 | `Some item A`
2 | `Some item B`
3 | `Some item C`
4 | `Some item D`
...
In such typical scenario, the many-to-many relationship between references and items is set in a junction table:
references_to_items
-----------------------
ref_id (FK) | item_id (FK)
-----------------------
1 | 4
2 | 1
3 | 2
4 | 1
...
In that scenario, it is easy to model and obtain all references that are associated to the same item, for instance item 1 has references 2 and 4 as per table above.
However, in my scenario, there is no items_table. But I would still want to model the fact that some references refer to the same (non-represented) item.
I see a possibility to model that via a many-to-many junction table as such (associating FKs of the references table):
reference_similarities
-----------------------
ref_id (FK) | ref_id_similar (FK)
-----------------------
2 | 4
2 | 8
2 | 9
...
Where references with ID 2, 4, 8 and 9 would be considered 'similar' for the purposes of my data model.
However, the inconvenience here is that such model requires to choose one reference (above id=2) as a 'pivot', to which multiple others can be declared 'similar' in the reference_similarities table. Ref 2 is similar to 4 and ref 2 is similar to 8 ==> thus 4 is similar to 8.
So the question is: is there a better design that doesn't involve having a 'pivot' FK as above?
Ideally, I would store the 'similarity' as an Array of FKs as such:
reference_similarities
------------------------
id | ref_ids (Array of FKs)
------------------------
1 | [2, 4, 8, 9]
2 | [1, 3, 5]
..but I understand from https://dba.stackexchange.com/questions/60132/foreign-key-constraint-on-array-member that it is currently not possible to have foreign keys in PostgreSQL arrays. So I'm trying to figure out a better design for this model.
I can understand that you want to group items in a set, and able to query the set from any of item in it.
You can use a hash function to hash a set, then use the hash as pivot value.
For example you have a set of values (2,4,8,9), it will be hashed like this:
hash = ((((31*1 + 2)*31 + 4)*31 + 8)*31 + 9
you can refer to Arrays.hashCode in Java to know how to hash a list of values.
int result = 1;
for (Object element : a)
result = 31 * result + (element == null ? 0 : element.hashCode());
Table reference_similarities:
reference_similarities
-----------------------
ref_id (FK) | hash_value
-----------------------
2 | hash(2, 4, 8, 9) = 987204
4 | 987204
8 | 987204
9 | 987204
To query the set, you can first query hash_value from ref_id first, then, get all ref_id from hash_value.
The draw back of this solution is every time you add a new value to a set, you have to rehash the set.
Another solution is you can just write a function in Python to produce a unique hash_value when creating a new set.
Ok, I deleted previous post and will try this again. I am sure I don't know the topic and I'm not sure if this is a loop or if I should use a stored function or how to get what I'm looking for. Here's sample data and expected output;
I have a single table A. Table has following fields; date created, unique person key, type, location.
I need a Postgres query that says for any given month(parameter, based on date created) and given a location(parameter based on location field), provide me fieds below where unique person key may be duplicated + or – 30 days from the date created within the month given for same type but all locations.
Example Data
Date Created | Unique Person | Type | Location
---------------------------------------------------
2/5/2017 | 1 | Admit | Hospital1
2/6/2017 | 2 | Admit | Hospital2
2/15/2017 | 1 | Admit | Hospital2
2/28/2017 | 3 | Admit | Hospital2
3/3/2017 | 2 | Admit | Hospital1
3/15/2017 | 3 | Admit | Hospital3
3/20/2017 | 4 | Admit | Hospital1
4/1/2017 | 1 | Admit | Hospital2
Output for the month of March for Hospital1:
DateCreated| UniquePerson | Type | Location | +-30days | OtherLoc.
------------------------------------------------------------------------
3/3/2017 | 2 | Admit| Hospital1 | 2/6/2017 | Hospital2
Output for the month of March for Hospital2:
None, because no one was seen at Hospital2 in March
Output for the month of March for Hospital3:
DateCreated| UniquePerson | Type | Location | +-30days | otherLoc.
------------------------------------------------------------------------
3/15/2017 | 3 | Admit| Hospital3 | 2/28/2017 | Hospital2
Version 1
I would use a WITH clause. Please, notice that I've added a column id that is a primary key to simplify the query. It's just to prevent the rows to be matched with themselves.
WITH x AS (
SELECT
id,
date_created,
unique_person_id,
type,
location
FROM
a
WHERE
location = 'Hospital1' AND
date_trunc('month', date_created) = date_trunc('month', '2017-03-01'::date)
)
SELECT
x.date_created,
x.unique_person_id,
x.type,
x.location,
a.date_created AS "+-30days",
a.location AS other_location
FROM
x
JOIN a
USING (unique_person_id, type)
WHERE
x.id != a.id AND
abs(x.date_created - a.date_created) <= 30;
Now a little bit of explanations:
First we select, let's say a reference data with a WITH clause. Think of it as a temporary table that we can reference in the main query. In given example it could be a "main visit" in given hospital.
Then we join "main visits" with other visits of the same person and type (JOIN condition) that happen in date difference of 30 days (WHERE condition).
Notice that the WITH query has the limits you want to check (location and date). I use date_trunc function that truncates the date to specified precision (a month in this case).
Version 2
As #Laurenz Albe suggested, there is no special need to use a WITH clause. Right, so here is a second version.
SELECT
x.date_created,
x.unique_person_id,
x.type,
x.location,
a.date_created AS "+-30days",
a.location AS other_location
FROM
a AS x
JOIN a
USING (unique_person_id, type)
WHERE
x.location = 'Hospital1' AND
date_trunc('month', x.date_created) = date_trunc('month', '2017-03-01'::date) AND
x.id != a.id AND
abs(x.date_created - a.date_created) <= 30;
This version is shorter than the first one but, in my opinion, the first is easier to understand. I don't have big enough set of data to test and I wonder which one runs faster (the query planner shows similar values for both).
Sorry if the post is in fact a duplicate. Just could not google anything similar and I am bit stuck on approach.
I am trying to populate cells in one sheet depending on date in rows of a different sheet, like these:
Sheet1 - entry sheet
ID | Name | Start date | End date
10 | Mike | 1.06.2016 | 2.06.2016
13 | Dido | 1.06.2016 | 5.06.2016
8 | Rene | 2.06.2016 | 20.06.2016
Sheet2 - report sheet
ids/dates | 1.06.2016 | 2.06.2016 | 3.06.2016 | date+1
8 | | Rene | Rene | Rene
10 | Mike | Mike | |
13 | Dido | Dido | Dido | Dido
Column Name cell's are to be populated in sheet2 depending on Sheet1 Column ID, Start date, end date. The position of the populated cell is defined in sheet2 by column ID and row Dates that should equal the same values in sheet1.
This report could be done with help of one formula. Please, check this Example File.
Assumptions
Suppose, you have Sheet1 with data:
Col A: ID
Col B: Name
Col C: Start date
Col D: End Date
Case 1. ID's are unique.
Go to Sheet2 and paste this formula in it:
={{"ids/dates";filter(Sheet1!A2:A,Sheet1!A2:A<>"")},{ArrayFormula(add(MIN(Sheet1!C:D),COLUMN(OFFSET(A1,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))-1));ArrayFormula(if(--(add(MIN(Sheet1!C:D),COLUMN(OFFSET(A1,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))-1)>=filter(Sheet1!C2:C,Sheet1!C2:C<>0))*--(add(MIN(Sheet1!C:D),COLUMN(OFFSET(A1,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))-1)<=filter(Sheet1!D2:D,Sheet1!C2:C<>0))=1,VLOOKUP(FILTER(Sheet1!A2:A,Sheet1!A2:A<>""),Sheet1!A:B,2,0),""))}}
That's all. Report will expand automatically when new data arrives on Sheet1. The report will return error if Data is not complete (misssing Names or dates) on Sheet1.
Case 2. ID's are NOT unique.
This solution works when ID's are not unique, ID's will be grouped together. One ID belongs to one person in this case.
The formula will be a bit longer:
={{"ids/dates";sort(UNIQUE(filter(Sheet1!A2:A,Sheet1!A2:A<>"")))},{ArrayFormula(add(MIN(Sheet1!C:D),COLUMN(OFFSET(A1,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))-1));ArrayFormula(if(QUERY(QUERY({filter(Sheet1!A2:A,Sheet1!A2:A<>""),ArrayFormula((--(add(MIN(Sheet1!C:D),COLUMN(OFFSET(A1,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))-1)>=filter(Sheet1!C2:C,Sheet1!C2:C<>0))*--(add(MIN(Sheet1!C:D),COLUMN(OFFSET(A1,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))-1)<=filter(Sheet1!D2:D,Sheet1!C2:C<>0))))},"select Col1, sum(Col"&JOIN("), sum(Col",ArrayFormula(COLUMN(OFFSET(B2,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))))&") group by Col1"),"Select Col"&JOIN(", Col",ArrayFormula(COLUMN(OFFSET(B2,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))))&" where Col1>0",0)=1,VLOOKUP(sort(UNIQUE(filter(Sheet1!A2:A,Sheet1!A2:A<>""))),Sheet1!A:B,2,0),""))}}
See example here.
Case 3. IDs are NOT unique. One ID <> one name
Here's working example, please check it. This case is the hardest one. We can have multiple IDs referring to multiple names. The final formula:
={{"ids/dates",ArrayFormula(add(MIN(Sheet1!C:D),COLUMN(OFFSET(A1,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))-1))};{sort(UNIQUE(FILTER(Sheet1!A2:A,Sheet1!A2:A<>""))),ArrayFormula(IFERROR(VLOOKUP(QUERY(QUERY({FILTER(Sheet1!A2:B,Sheet1!A2:A<>""),ArrayFormula(--(add(MIN(Sheet1!C:D),COLUMN(OFFSET(A1,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))-1)>=filter(Sheet1!C2:C,Sheet1!C2:C<>0))*--(add(MIN(Sheet1!C:D),COLUMN(OFFSET(A1,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))-1)<=filter(Sheet1!D2:D,Sheet1!C2:C<>0))*row(OFFSET(A1,,,rows(FILTER(Sheet1!A2:B,Sheet1!A2:A<>"")))))},"select Col1, sum(Col"&JOIN("), sum(Col",ArrayFormula(COLUMN(OFFSET(C1,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))))&") group by Col1"),"Select Col"&JOIN(", Col",ArrayFormula(COLUMN(OFFSET(B2,,,1,MAX(Sheet1!C:D)-MIN(Sheet1!C:D)))))&" where Col1>0",0),{ArrayFormula(row(OFFSET(A1,,,rows(FILTER(Sheet1!A2:B,Sheet1!A2:A<>""))))),FILTER(Sheet1!A2:B,Sheet1!A2:A<>"")},3,0)))}}
The formula will work incorrectly if two Date ranges intersect:
102 Mike 6/21/2016 6/27/2016
102 Mike 6/11/2016 6/22/2016
I'm implementing a simple search in postgresql that will be used to retrieve typeahead results on a web page. So, I need the last argument to use starts-with matching, since the user may not have finished typing the word. When I construct my tsquery, I'm adding :* to the last argument. Here's a sample query:
SELECT id, key, name
FROM principal,
to_tsvector(key || ' ' || name) vector,
to_tsquery('investig:*') query
WHERE vector ## query
ORDER BY ts_rank(vector, query) DESC
While typing the word "investigate", I get the following behavior:
Input | Result Count
==========================
i | 0
in | 0
inv | 8
inve | 8
inves | 8
invest | 8
investi | 7
investig | 7
investiga | 0
investigat | 0
investigate | 7
This is better than if I omit the :*, but not good enough. Why do I get 0 results for investiga when investigate returns 7 results? Is there a better way to construct my query to make sure I get everything that begins with a search term?
On my database table I have
Key | Value
a | 1
a | 2
b | 11
c | 1
d | 2
b | 3
But I just need to get the items which keys are not duplicates of the previous rows. The desired result should be:
Key | Value
a | 1
b | 11
c | 1
d | 2
How could we get the desired result using entity-framework?
Note: we need the first value. Thank you very much.
var q = from e in Context.MyTable
group e by e.Key into g
select new
{
Key = g.Key,
Value = g.OrderBy(v => v.Value).FirstOrDefault()
};
You should look at either writing a View in the database and mapping your entity to that.
Or creating a DefiningQuery in the part of your EDMX (aka the bit that ends up in the SSDL file).
See Tip 34 for more information.
Conceptually both approaches allow you to write a view that excludes the 'duplicate rows'. The difference is just where the view lives.
If you have control over the database - I'd put the view in the database
If not you can put the view in your inside the and then map to that.
Hope this helps
Alex