I am using JPA and Hibernate, but my need is too complicated to build a HQL, at least for me.
I decided to use native SQL.
I need to get some records/entities with their child lists but, i need to filter childs, i do not want all the childs.
Is this possible?
For example i have three tables like
conversation_table:
id
mail_table:
id, conversation_id, sender_id
user_table:
id, married_bool
I need conversation entities having lists that filled by mails those are send by married users.
I tried so far
Select * from conversation_table join mail_table on ( mail_table.sender_id=user_table.id and user_table.married_bool=true)
I am getting an error like:
user_table is unknown
I tried
Select * from (conversation_table, user_table, mail_table) join mail_table on ( mail_table.sender_id=user_table.id and user_table.married_bool=true)
I am getting
mail_table is non unique table/alias
This is only a light example, also need to fill some entity lists of mail entity in other tables for example recipient_table, i think i have to add join clauses for filling these too in native query, am i right? Also i am getting 'not known'/'non unique alias' errors, when try this additional join clauses.
Thanks for suggestions.
Something like this:
SELECT *
FROM conversation_table CT
JOIN mail_table MT
ON CT.Id = MT.conversation_id
JOIN user_id UI
ON MT.sender_id=UI.id
WHERE UT.married_bool = 1
If you really want to use Hibernate ORM for this query they Criteria Query is the best approach for this. Recently, i have the same requirement and have used Criteria only.
Related
I am trying to retrieve every data stored in 2 tabs from my database through a SELECT statement.
The problem is there are a lot of columns in each tab and manually selecting each column would be a pain in the ass.
So naturally I thought about using a join :
select * from equipment
join data
on equipment.id = data.equipmentId
The problem is I am getting the equipment ID 2 times in the result.
I thought that maybe some specific join could help me filter out the duplicate key, but I can't manage to find a way...
Is there any way to filter out the foreign key or is there a better way to do the whole thing (I would rather not have to post process the data to manually remove those duplicate columns)?
You can use USING clause.
"The USING clause specifies which columns to test for equality when
two tables are joined. It can be used instead of an ON clause in the
JOIN operations that have an explicit join clause."
select *
from test
join test2 using(id)
Here is a demo
You can also use NATURAL JOIN
select *
from test
natural join test2;
Okay, I'm relatively new to the more advanced uses of SQL Server.
I have several tables that I need to gather informations from, and several of these tables links to other tables where I need a specific information. As a result, I just want one row with all the information, preferential named with aliases.
For example:
Tab_Transcoders:
ID, VideoCamID, InputStreamID, OutputStreamID.
where InputStream links to another table where I need the row of the matching ID, where in this row are other ID's (e.g. StreamType_ID that belongs to a third table containing ID_StreamType and Description etc.)
Same with OutputStreamID, same with VideoCamID.
In the end, I need a row containing for example:
ID, VideoCamID, InputStreamID, InputStreamType, InputStreamTypeDesc,
OutputStreamID, OutputStreamType, OutputStreamDesc, VideoCamID, etc. etc. etc.
It is important for me that I can set aliases, as for example InputStreamID & OutputStreamID links to the same table where all my Streams are listed (with IP's, Descs..)
I can accomplish this with doing like 100 SELECTS & SUBSELECTS, but I don't think that's an appropriate way.
I read some informations about things like CURSOR, UNION, FETCH, JOIN etc. etc.. but I don't know which one I have to use for my purpose.
eli
I think you want something like the following....
Select
t.ID,
t.VideoCamID,
i.InputStreamID,
is.StreamType as InputStreamType,
is.StreamDesc as InputStreamDesc,
o.OutputStreamID,
os.StreamType as OutputStreamType,
os.StreamDesc as OutputStreamDesc,
v.VideoCamID
from
Tab_Transcoders t
inner join InputStreams i on i.InputStreamID=t.InputStreamId
inner join Streams is on is.StreamId=i.StreamId
inner join OutputStreams o on o.OutputStreamId=t.OutputStreamId
inner join Streams os on os.StreamID=o.StreamId
inner join VideoCams v on v.VideoCamId=t.VideoCamID
If there is a defined relationship between your tables, then Use Join.
e.g Customer Order
Order will have customer Id
Select Order.ID,Order.Quantity, Order.CustomerId, Customer.FullName, Customer.Address
From Orders Order
Join
Customer
On
Order.CustomerId = Customer.CustomerId
First start by getting data from two tables using the join and then if it works as per your requirement, add another required table in the join.
Read about SQl JOINS.. It is fairly simple.
I will recommend reading you some of the articles around CTE aka Common Table Expression.
Refer http://msdn.microsoft.com/en-us/library/ms190766%28v=sql.105%29.aspx.
Apart from this never use subqueries. Try to use inner join / any other join if possible.
How can I create the following SQL statement in Nhibernate using CreateCriteria:
SELECT distinct top 20 a.* from ActivityLog a
left join WallPost w on a.ActivityLogId = w.ActivityLogId left join ItemStatus i on i.StatusId = w.ItemStatus
I always tend to get all columns from all tables returned in the sql statement producing duplicates even though I map it to the ActivityLog table. I am also doing paging as the code below shows:
ICriteria crit = nhelper.NHibernateSession.CreateCriteria(typeof(Model.ActivityLog), "a").CreateAlias("a.WallPosts", "w",CriteriaSpecification.LeftJoin)
.CreateAlias("w.ItemStatus", "i", CriteriaSpecification.LeftJoin)
.SetMaxResults(pageSize).SetFirstResult(startRow).AddOrder(Order.Desc("a.Date"));
Thanks
H
Sounds like you have set lazy loading to false in your mapping files meaning that all the associations and child collections are being loaded up too. Can you verify that?
You ask "How to select one table using NHibernate CreateQuery" (HQL). In that case you can choose what to fetch using select.
In your text you're using criteria. AFAIK, you cannot directly control what columns you want to read. However, if you create a DetachedCriteria for the join, this won't be fetched.
I have 6 tables, let's call them a,b,c,d,e,f. Now I want to search all the colums (except the ID columns) of all tables for a certain word, let's say 'Joe'. What I did was, I made INNER JOINS over all the tables and then used LIKE to search the columns.
INNER JOIN
...
ON
INNER JOIN
...
ON.......etc.
WHERE a.firstname
~* 'Joe'
OR a.lastname
~* 'Joe'
OR b.favorite_food
~* 'Joe'
OR c.job
~* 'Joe'.......etc.
The results are correct, I get all the colums I was looking for. But I also get some kind of cartesian product, I get 2 or more lines with almost the same results.
How can i avoid this? I want so have each line only once, since the results should appear on a web search.
UPDATE
I first tried to figure out if the SELECT DISTINCT thing would work by using this statement: pastie.org/970959 But it still gives me a cartesian product. What's wrong with this?
try SELECT DISTINCT?
On what condition do you JOIN this tables? Do you have foreign keys or something?
Maybe you should find that word on each table separately?
What kind of server are you using? Microsoft SQL Server has a full-text index feature (I think others have something like this too) which lets you search for keywords in a much less resource-intensive way.
Also consider using UNION instead of joining the tables.
Without seeing your tables, I can only really assume what's going on here is you have a one-to-many relationship somewhere. You probably want to do everything in a subquery, select out the distinct IDs, then get the data you want to display by ID. Something like:
SELECT a.*, b.*
FROM (SELECT DISTINCT a.ID
FROM ...
INNER JOIN ...
INNER JOIN ...
WHERE ...) x
INNER JOIN a ON x.ID = a.ID
INNER JOIN b ON x.ID = b.ID
A couple of things to note, however:
This is going to be sloooow and you probably want to use full-text search instead (if your RDBMS supports it).
It may be faster to search each table separately rather than to join everything in a Cartesian product first and then filter with ORs.
If your tables are entity type tables, for example a being persons and b being companies, I don't think you can avoid a cartesian product if you search for the results in this way (single query).
You say you want to search all the tables for a certain word, but you probably want to separate the results into the corresponding types. Right? Otherwise a web search would not make much sense.
So if you seach for 'Joe', you want to see persons containing the name 'Joe' and for example the company named 'Joe's gym'. Since you are searching for different entities so you should split the search into different queries.
If you really want to do this in one query, you will have to change your database structure to accommodate. You will need some form of 'search table' containing an entity ID (PK) and entity type, and a list of keywords you want that entity to be found with. For example:
EntityType, EntityID, Keywords
------------------------------
Person, 4, 'Joe', 'Doe'
Company, 12, 'Joe''s Gym', 'Gym'
Something like that?
However it's different when your search returns only one type of entity, say a Person, and you want to return the Persons for which you get a hit on that keyword (in any related table to that Person). Then you will need to select all the fields you want to show and group by them, leaving out the fields in which you are searching. Including them inevitably leads to a cartesian product.
I'm just brainstorming here, by the way. It hope it's helpful.
I've got a database with three tables: Books (with book details, PK is CopyID), Keywords (list of keywords, PK is ID) and KeywordsLink which is the many-many link table between Books and Keywords with the fields ID, BookID and KeywordID.
I'm trying to make an advanced search form in my app where you can search on various criteria. At the moment I have it working with Title, Author and Publisher (all from the Book table). It produces SQL like:
SELECT * FROM Books WHERE Title Like '%Software%' OR Author LIKE '%Spolsky%';
I want to extend this search to also search using tags - basically to add another OR clause to search the tags. I've tried to do this by doing the following
SELECT *
FROM Books, Keywords, Keywordslink
WHERE Title LIKE '%Joel%'
OR (Name LIKE '%good%' AND BookID=Books.CopyID AND KeywordID=Keywords.ID)
I thought using the brackets might separate the 2nd part into its own kinda clause, so the join was only evaluated in that part - but it doesn't seem to be so. All it gives me is a long list of multiple copies of the one book that satisfies the Title LIKE '%Joel%' bit.
Is there a way of doing this using pure SQL, or would I have to use two SQL statements and combine them in my app (removing duplicates in the process).
I'm using MySQL at the moment if that matters, but the app uses ODBC and I'm hoping to make it DB agnostic (might even use SQLite eventually or have it so the user can choose what DB to use).
You need to join the 3 tables together, which gives you a tablular resultset. You can then check any columns you like, and make sure you get distinct results (i.e. no duplicates).
Like this:
select distinct b.*
from books b
left join keywordslink kl on kl.bookid = b.bookid
left join keywords k on kl.keywordid = k.keywordid
where b.title like '%assd%'
or k.keyword like '%asdsad%'
You should also try to avoid starting your LIKE values with a percent sign (%), as this means SQL Server can't use an index on that column and has to perform a full (and slow) table scan. This starts to make your query into a "starts with" query.
Maybe consider the full-text search options in SQL Server, also.
What you've done here is made a cartesian result set by having the tables joined with the commas but not having any join criteria. Switch your statements to use outer join statements and that should allow you to reference the keywords. I don't know your schema, but maybe something like this would work:
SELECT
*
FROM
Books
LEFT OUTER JOIN KeywordsLink ON KeywordsLink.BookID = Books.CopyID
LEFT OUTER JOIN Keywords ON Keywords.ID = KeywordsLink.KeywordID
WHERE Books.Title LIKE '%JOEL%'
OR Keywords.Name LIKE '%GOOD%'
Use UNION.
(SELECT Books.* FROM <first kind of search>)
UNION
(SELECT Books.* FROM <second kind of search>)
The point is that you could write two (or more) simple and efficient queries instead of one complicated query that tries to do everything at once.
If number of resulting rows is low, then UNION will have very little overhead (and you can use faster UNION ALL if you don't have duplicates or don't care about them).
SELECT * FROM books WHERE title LIKE'%Joel%' OR bookid IN
(SELECT bookid FROM keywordslink WHERE keywordid IN
(SELECT id FROM keywords WHERE name LIKE '%good%'))
Beware that older versions of MySQL didn't like subselects. I think they've fixed that.
You must also limit the product of the join by specifying something like
Books.FK1 = Keywords.FK1 and
Books.FK2 = Keywordslink.FK2 and
Keywords.FK3 = Keywordslink.FK3
But i don't know your exact data model so your solution may be slightly different.
I'm not aware of any way to accomplish a "conditional join" in SQL. I think you'll be best served with executing the two statements separately and combining them in the application. This approach is also more likely to stay DB-agnostic.
It looks like Neil Barnwell has covered the answer that I would have given, but I'll add one thing...
Books can have more than one author. If your data model is really designed as your query implies you might want to consider changing it to accommodate that fact.