I am writing a cypher query in neo4j that merge few seperate queries with'UNION' operator. Now, the final result need to be sorted according to a specific column and I also need to be able to use 'LIMIT' to the final result so that I can fetch based on pagination request.
How to achieve that? adding 'ORDER BY' or 'LIMIT' at the end doesn't seems to work. Can't find a way to wrap the result as temporary set(as in sql queries) either. Any suggestions?
Currently it is not possible to add a ORDER BY or SKIP/LIMIT clause to the global set of UNION.
This is a pending feature request, see https://github.com/neo4j/neo4j/issues/2725
Maybe you can share your query and we can find a way to do it without UNION ?
Related
I have a requirement which is somewhat similar to this. My API supports a filter where there is more than 8 filter parameter. So, I want to create a query dynamically based on the filter parameter passed. I am using CriteriaBuilder to create a dynamic query.
Now, I am able to create dynamic queries successfully but the issue comes when the user wants to sort on an aggregate functions. In my query, I have 4 aggregate (count) function. So to support sorting on these columns, I just use the expression of this aggregate function but what I want is to use the alias of this expression
Repeating the expression in select and order by doesn't seem right to me. So, is there a solution/workaround to the problem. I want to declare the expression alias once and use it in both select and order by clause and if required in my group by clause in future
You probably need to build a custom projection class, you can find a decent and easy one, SQLProjectionWithAliasSupport in https://hibernate.atlassian.net/browse/HHH-2952 (from Sergey Pulyaev)
If then one wants to support also sub criteria, things get more complicate
I am using gorm to interact with a postgres database. I'm trying to ORDER BY a query that uses DISTINCT ON and this question documents how it's not that easy to do that. So I need to end up with a query in the form of
SELECT * FROM (<subquery>) ORDER BY column;
At first glance it looks like I need to use db.QueryExpr() to turn the query I have into an expression and build another query around it. However it doesn't seem gorm has an easy way to directly specify the FROM clause. I tried using db.Model(expr) or db.Table(fmt.Sprint(expr)) but Model seems to be completely ignored and fmt.Sprint(expr) doesn't return exactly what I thought. Expressions contain a few private variables. If I could turn the original query into a completely parsed string then I could use db.Table(query) but I'm not sure if I can generate the query as a string without running it.
If I have a fully built gorm query, how can I wrap it in another query to do the ORDER BY I'm trying to do?
If you want to write raw SQL (including one that has a SQL subquery) that will be executed and the results added to an object using gorm, you can use the .Raw() and .Scan() methods:
query := `
SELECT sub.*
FROM (<subquery>) sub
ORDER BY sub.column;`
db.Raw(query).Scan(&result)
You pass a pointer reference to an object to .Scan() that is structured like the resulting rows, very similarly to how you would use .First(). .Raw() can also have data added to the query using ? in the query and adding the values as comma separated inputs to the function:
query := `
SELECT sub.*
FROM (<subquery>) sub
WHERE
sub.column1 = ?
AND sub.column2 = ?
ORDER BY sub.column;`
db.Raw(query, val1, val2).Scan(&result)
For more information on how to use the SQL builder, .Raw(), and .Scan() take a look at the examples in the documentation: http://gorm.io/advanced.html#sql-builder
Is it possible to use Xpath or Xquery to query XML type fields in a database using Eloquent ORM ? I find in inconvenient to parse the XML every time and filter my results in memory. I would rather return my results from a query, is there a way to achieve that using Eloquent or I'm stuck with raw database statements?
Thank you
I reviewed the options for selecting items in Eloquent and there is not much good options to select based on XML values as you expect. You can use some wildcards and run calculations on Eloquent to filter needed data but none of these are very efficient.
I Just want to make sure I understand this correctly...
search is an object that contains a querystring.
Repo.Query returns an ObjectQuery<T>.
From my understanding the chained linq statements will filter the results after entity framework has returned all the rows satisfying the query. So really ALL the rows are being returned and THEN filtered in memory. So we are returning a bunch of data that we don't really want. There's about 10k rows being returned so this is kind of important. Just like to get my confusion cleared up.
var searchQuery = Repo.Query(search)
.Where(entity =>
entity.Prop1.ToUpper().Equals(prop1.ToUpper()) &&
entity.Prop2.ToUpper().Equals(prop2.ToUpper()))
.OrderBy(entity => Repo.SortExpression ?? entity.prop1);
Your Repo.Query(string query) function should return IQueryable<T>.
Then you can filter and order without getting all rows first.
IQueryable(Of T) Interface
hope this helps
If this is to SQL, this will most likely create a SQL query and filter on the server and not in memory.
As a matter of fact, the statement above wouldn't actually do anything.
It's only when you iterate over it that the query will be executed. This is why certain providers (like the EF to SQL one) can collapse expression trees into a SQL query.
Easiest way to check is to use LINQPAD or the SQL Profiler to see what query is actually is executed.
I am quite sure that DQL will be the way to go, but I am wondering if Doctrine, i am using Doctrine 2, has someway to return the row count. I won't be using the rows itself, I just want the count.
I'm new to Doctrine2 but it looks like you can simply do this:
$query = $em->createQuery('SELECT COUNT(u.id) FROM Entities\User u');
$count = $query->getSingleScalarResult();
Source (Using Agregate Functions): http://www.doctrine-project.org/docs/orm/2.0/en/reference/dql-doctrine-query-language.html#dql-select-examples
Allowed aggregate functions: http://www.doctrine-project.org/docs/orm/2.0/en/reference/dql-doctrine-query-language.html#aggregate-functions
Here is another interesting point of view about using aggregated functions in DQL
http://doctrine-orm.readthedocs.org/en/latest/cookbook/aggregate-fields.html
Maybe you would avoid the creation of an specific query to obtain an aggregate value. In this case, aggregate fields are a good alternative.