I'm wondering about the best way to perform a SQL query.
I have a table which contains SUBJECTS which are related to ARTICLES (each article contains at least 2 SUBJECTS).
The user is searching for two SUBJECTS and I need to reply with all articles.
I have a table which looks like this:
SubjectID ---> key
ArticleID
My query is as follows:
SELECT ArticleID
FROM tblSubjectsInArticles
WHERE SubjectID = #pSubjectID1
AND ArticleID IN (SELECT ArticleID FROM tblSubjectsInArticles WHERE SubjectID = #pSubjectID2);
I got a feeling that there is a better way to perform this task, maybe an efficient query or a different data structure. Maybe one of you guys know a better way or you can reassure that this is the best way. Thanks.
select distinct s1.ArticleID
from tblSubjectsInArticles s1
join tblSubjectsInArticles s2
on s1.ArticleID = s2.ArticleID
where s1.SubjectID = #pSubjectID1
and s2.SubjectID = #pSubjectID2
So you would create a joined table on the ArticleIDs and filter on the related subjects. The distinct makes sure your list contains only unique ArticleIDs
Related
I have two tables called resource and resource_owners.
The resource_owners table contains two columns called resource_id and owner_id.
resource_id | owner_id |
-------------+-----------
The resource table contains two relevant columns: parentresource_id and id.
parentresource_id | id |
-------------------+------
resource_owners.resource_id, resource.id and resource.parentresource_id are all join columns between the two tables. Now what I want to do is the following:
For every row in the resource table, take the value in id, match it with a corresponding resource_owners.resource_id, retrieve the corresponding resource_owners.owner_id value (call it $owner_value), then set resource_owners.owner_id to $owner_value where resource_owners.resource_id equals resource.parentresource_id.
In conversational terms, this is what I want to do: For each resource, I want to re-assign the parent-resource's owner_id to be the resource's owner_id.
I've tried to wrap my head around this problem and it looks like I'll need two different table joins (resource.id with resource_owners.resource_id and resource.parentresource_id with resource_owners.resource_id).
Can someone point me in the right direction? Is what I want even possible with a single query? I'm okay with a PostgreSQL script as well if that works better for my use case.
I'm not sure what database you are using but you should be able to accomplish using the logic below if I understood your question correctly:
UPDATE RESOURCE_OWNER SET
OWNER_ID = UP.OWNER_ID
FROM (SELECT rc.ID, TMP.OWNER_ID FROM (SELECT RSC.ID, ROWRS.OWNER_ID, ROWRS.RESOURCE_ID FROM RESOURCE RSC JOIN RESOURCE_OWNER ROWRS
ON RSC.ID = ROWRS.RESOURCE_ID) TMP JOIN RESOURCE rc on rc.PARENTRESOURCE_ID = TMP.RESOURCE_ID) UP WHERE RESOURCE_OWNER.RESOURCE_ID = UP.ID;
First I need to say that it is safe to assume that I have no formal education in SQL although I have education in relational algebra.
I am investigating what would be the best approach to the following problem.
Our database is holding texts and keywords for every text.
Articles
id | text
Keywords
id | word
Articles_keywords
id_article | id_keyword
For the sake of this question the provider of answer can assume that tables are indexed however one wants.
So the problem is getting all articles that have a specific keyword.
I have talked with 2 groups of people that solve this in 2 ways, and they both claim that the approach of other group is wrong.
First solution using the IN operator:
SELECT * FROM Articles AS a WHERE a.id IN
(SELECT id_article FROM Articles_Keywords AS ak WHERE ak.id_keyword IN
(SELECT id FROM keywords AS k WHERE k.word = 'xyz'));
Other solution is using JOIN operator of course:
SELECT * FROM Articles as a
JOIN Articles_Keywords as ak
ON a.id = ak.id_article
JOIN Keywords as k
ON k.id = ak.id_keyword
WHERE k.word = 'xyz';
Which approach is better and, above all, why?
Edit
In articles table we have an id column being unique and, just for the sake of this question we could assume that there are no duplicate texts.
The same thing goes for the keywords table.
In article_keywords table the ordered pair (id_article,id_keyword) is unique
Good morning/afternoon! I was hoping someone could help me out with something that probably should be very simple.
Admittedly, I’m not the strongest SQL query designer. That said, I’ve spent a couple hours beating my head against my keyboard trying to get a seemingly simple three way join working.
NOTE: I'm querying a Vertica DB.
Here is my query:
SELECT A.CaseOriginalProductNumber, A.CaseCreatedDate, A.CaseNumber, B.BU2_Key as BusinessUnit, C.product_number_desc as ModelNumber
FROM pps_sfdc.v_Case A
INNER JOIN reference_data.DIM_PRODUCT_LINE_HIERARCHY B
ON B.PL_Key = A.CaseOriginalProductLine
INNER JOIN reference_data.DIM_PRODUCT C
ON C.product_line_code = A.CaseOriginalProductLine
WHERE B.BU2_Key = 'XWT'
LIMIT 20
I have a view (v_Case) that I’m trying to join to two other tables so I can lookup a value from each of them. The above query returns identical data on everything EXCEPT the last column (see below). It's like it's iterating through the last column to pull out the unique entries, sort of like a "GROUP BY" clause. What SHOULD be happening is that I get unique rows with specific "BusinessUnit" and "ModelNumber" for that record.
DUMEPRINT 5/2/2014 8:56:27 AM 3002845327 JJT Product 1
DUMEPRINT 5/2/2014 8:56:27 AM 3002845327 JJT Product 2
DUMEPRINT 5/2/2014 8:56:27 AM 3002845327 JJT Product 3
DUMEPRINT 5/2/2014 8:56:27 AM 3002845327 JJT Product 4
I modeled my solution after this post:
How to deal with multiple lookup tables for beginners of SQL?
What am I doing wrong?
Thank you for any help you can provide.
Data issue. General rule in trouble shooting these is the column that is distinct (in this case C.product_number_desc as ModelNumber) for each record is generally where the issue is going to be...and why I pointed you towards dim_product.
If you receive duplicates, this query below will help identify if this table is giving you the issues. Remember key in this statement can be multiple fields...whatever you are joining the table on:
Select key,count(1) from table group by key having count(1)>1
Other options for the future...don't assume it's your code, duplicates like this almost always point towards dirty data (other option is you are causing cross joins because keys are not correct). If you comment out the 'c' table and the column referred to in the select clause, you would have received one row...hence your dupes were coming from the 'c' table here.
Good luck with it
Okay, so I've got two tables. One table (table 1) contains a column Books_Owned_ID which stores a series of numbers in the form of 1,3,7. I have another table (table 2) which stores the Book names in one column and the book ID in another column.
What I want to do is create an SQL code which will take the numbers from Books_Owned_IDand display the names of those books in a new column. Like so:
|New Column |
Book 1 Name
Book 2 Name
Book 3 Name
I can't wrap my head around this, it's simple enough but all the threads I look on get really confusing.
Table1 contains the following columns:
|First_Name| Last_Name| Books_Owned_ID |
Table2 contains the following columns:
|Book_Name|Book_ID|
You need to do an inner join. This is a great example/reference for these
SELECT Book_Name FROM Table2
INNER JOIN Table1
ON Table1.Books_Owned_ID = Table2.Book_ID
EDIT SQL Fiddle
I will work on getting the column comma split working. It wont be a lot extra for this.
EDIT 2 See this answer to build a function to split your string. Then you can do this:
SELECT Book_Name FROM Table2
WHERE Book_ID IN(SELECT FN_ListToTable(',',Table1.Books_Owned_ID) FROM Table1 s)
The core of this centers around data normalisation... Each fact is stored only once (and so is "authoritative"). You should also get into the habit of only storing a single fact in any field.
So, imagine the following table layouts...
Books
Id, Name, Description
Users
Id, Username, EmailAddress, PasswordHash, etc....
BooksOwned
UserId, BookId
So if a single user owns multiple books, there will be multiple entries in the BooksOwned table...
UserId, BookID
1, 1
1, 2
1, 3
Indicates that User 1 owns books 1 through 3.
The reason to do it this way is that it makes it much easier to query in future. You also treat BookId as an Integer instead of a string containing a list - so you don't need to worry about string manipulation to do your query.
The following would return the name of all books owned by the user with Id = 1
SELECT Books.Name
FROM BooksOwned
INNER JOIN Books
ON BooksOwned.BookId = Books.Id
WHERE BooksOwned.UserId = 1
You need a function which takes a comma separated list and returns a table. This is slow and fundamentally a bad idea. Really all this does is convert this way of doing it to be like the data model I describe below. (see ProfessionalAmateur's answer for an example of this).
If you are just starting change your data model. Make a linking table. Like this:
Okay, so I've got two tables. One table (table 1) contains a column Books_Owned_ID which stores a series of numbers in the form of 1,3,7. I have another table (table 2) which stores the Book names in one column and the book ID in another column.
What I want to do is create an SQL code which will take the numbers from Books_Owned_IDand display the names of those books in a new column. Like so:
Person Table
|First_Name| Last_Name| Person_ID |
Book Table
|Book_Name|Book_ID|
PersonBook Table
|PersonID|BookID|
This table can have more than one row for each person.
Although I'm using Rails, this question is more about database design. I have several entities in my database, with the schema a bit like this: http://fishwebby.posterous.com/40423840
If I want to get a list of people and order it by surname, that's no problem. However, if I want to get a list of people, ordered by surname, enrolled in a particular group, I have to use an SQL statement that includes several joins across four tables, something like this:
SELECT group_enrolment.*, person.*
FROM person INNER JOIN member ON person.id = member.person_id
INNER JOIN enrolment ON member.id = enrolment.member_id
INNER JOIN group_enrolment ON enrolment.id = group_enrolment.enrolment_id
WHERE group_enrolment.id = 123
ORDER BY person.surname;
Although this works, it strikes me as a bit inefficient, and potentially as my schema grows, these queries could get more and more complicated.
Another option could be to join the person table to all the other tables in the query by including person_id in the other tables, then it would just be one single join, for example
SELECT group_enrolment.*, person.*
FROM person INNER JOIN group_enrolment ON group_enrolment.person_id
WHERE group_enrolment.id = 123
ORDER BY person.surname;
But this would mean that in my schema, the person table is joined to a lot of other tables. Aside from a complicated schema diagram, does anyone see any disadvantages to this?
I'd be very grateful for any comments on this - whether what I'm doing now (the many table join) or the second solution or another one that hasn't occurred to me is the best way to go.
Many thanks in advance
Well, joins are what databases do. Having said that, you may consider propagating natural keys in your model, which would then allow you to skip over some tables in joins. Take a look at this example.
EDIT
I'm not saying that this will match your model (problem), but just for fun try similar queries on something like this: