I have a data table Employees, I want to show the employee name, the employee number, the manager number and the manager name of the employee who has the least salary in the company. I decide to perform a self join, and here's my code:
select worker.employee_id, worker.last_name "Worker Last Name",
worker.salary manager.last_name "Manager Last Name", manager.manager_id
from employees worker join employees manager
on worker.manager_id = manager.employee_id
having worker.salary = (select min(salary)
from employees);
However, when I run this, the error "from keyword not found where expected" pops up. What should I do?
Oops, realized my own mistakes. I forgot to place a comma between worker.salary and manager.last_name, and I should not have WHERE instead of HAVING.
select worker.employee_id, worker.last_name "Worker Last Name",
worker.salary, manager.last_name "Manager Last Name", manager.manager_id
from employees worker join employees manager
on worker.manager_id = manager.employee_id
where worker.salary = (select min(salary)
from employees);
After fixing those two mistakes, the code runs fine.
Related
I'm trying to do the following query in linq, however I'm getting an exception error, though my query looks fine to me. So here is the story:
Diagram
I have a many to many relationship between the users and the organizations. A user can be a part of many organizations, and an organization can have many users.
What Im trying to query
So given a user id, i want to query all the team members (users) i have in all the organizations i belong to. So
Input: User X id (guid), and this user belongs to Organization A, and Organization B
Output:
User A, Organization A
User B, Organization A
User C, Organization B
The Actual Query
I though this would do just that
var user = db.Users.Include(q => q.UserOrganization).SingleOrDefault( q => q.Id == id.ToString());
var members = (from us in db.Users.Include(q => q.UserOrganization)
let orgs = user.UserOrganization.Select(z => z.OrganizationId)
where us.UserOrganization.Any(q => orgs.Contains(q.OrganizationId) )
select new UserResource{
id = Guid.Parse(us.Id),
email = us.Email
}
).ToArray();
My query fails on the where clause, with the error:
Processing of the LINQ expression 'AsQueryable<long>((Unhandled parameter: __Select_0))' by 'NavigationExpandingExpressionVisitor' failed. This may indicate either a bug or a limitation in EF Core
Not sure what to change in the query. Please help.
PS: I wrote the query initially in MySql as follows:
SELECT UU.`Id`, UU.`Email`, UUO.`OrganizationId`
FROM aspnetusers AS UU
LEFT JOIN userorganization AS UUO ON UUO.`UserId` = `UU`.Id
WHERE UUO.`OrganizationId` IN
(
SELECT UO.`OrganizationId` FROM aspnetusers AS U
LEFT JOIN userorganization AS UO ON UO.UserId = U.Id
WHERE u.Id = '6caa67e7-69f3-49a3-ad61-10b07d379f10'
)
AND UU.Id != '6caa67e7-69f3-49a3-ad61-10b07d379f10'
The "SingleOrDefault" always executes the Query. User is not an IQueryable.
So the let orgs = user.UserOrganization.Select(z => z.OrganizationId) cannot be translated to SQL, do your var orgs = user.UserOrganization.Select(z => z.OrganizationId) before the Query, in Plain C#. This cannot be used in SQL-Queries.
With orgs being an IList<int> it will work.
But it should be prefered to find a solution that can be solved with one query only. Here you have two.
The SingleOrDefault might be not useful, you go better without, than you have a simple IQueryable. And The "Any" can most often be realized with a simple (Inner) Join, returning only values, if you have a match between to tables. That is the Same as Where - Any - Contains
I have three tables
SalesDetails with columns SalesId, ProductId, Qty, Price etc
SalesPersonDtls with columns SalesId, SalesPersonId, CommPercentage etc
SalesPerson with columns SalesPersonId, firstName, lastName etc
I have second table because one sale can be done by more than one sales person together with split commission.
I have various inputs in search screen like productname, sales date, sales person name etc.
I am making the model class as 'AsQueryable' and add various where conditions and finally the result into a list.
I have sales person's name in search criteria but I don't know how to include this into the search. Can you please help?
Thanks
Peter
Peter
If I get it correct , relation of your business models is like this :
person (n) <-----> (1) Sale (1) <-----> (n) Details
you put sale and person relation in "SalesPersonDtls" and sale and detail relation to "SalesDetails". I think it's better to change your entities a little bit, if you want to get better result as your project getting bigger and more complex.
Your entities should be like this :
Sale
{
List<SalesDetail> details;
List<Person> persons;
...
}
SalesDetail
{
Sale
...
}
Person
{
Sale
name
...
}
Now it's really simple , if you want sales that is related to a personName :
sales.Where(sale => sale.Persons.Any(person => person.PersonName == "your input name"));
UPDATE :
If you can't or don't want to change your models:
first you need to find personId by it'name and then search into your "SalesPersonDtls" and get saleIds.
Entity relation: Transaction(#ManyToOne - eager by default) -> Account
String sql = "SELECT new com.test.Pojo(t.account, SUM(t.value)) FROM Transaction t GROUP BY t.account";
List list = entityManager.createQuery(sql).getResultList();
By default JPA using Hibernate implementation will generate 1 + n queries. The n queries are for lazy loading of the account entities.
How can I make this query eager and load everything with a single query? The sql equivalent would be something like
SELECT account.*, SUM(t.value) FROM transactions JOIN accounts on transactions.account_id = accounts.id GROUP BY account.id
, a syntax that works well on PostgreSQL. From my findings Hibernate is generating a query that justifies the lazy loading.
SELECT account.id, SUM(t.value) FROM transactions JOIN accounts on transactions.account_id = accounts.id GROUP BY account.id
Try marking the #ManyToOne field as lazy:
#ManyToOne(fetch = FetchType.LAZY)
private Account account;
And change your query using a JOIN FETCH of the account field to generate only one query with all you need, like this:
String sql = "SELECT new com.test.Pojo(acc, SUM(t.value)) "
+ "FROM Transaction t JOIN FETCH t.account acc GROUP BY acc";
UPDATE:
Sorry, you're right, the fetch attribute of #ManyToOne is not required because in Hibernate that is the default value. The JOIN FETCH isn't working, it's causing a QueryException: "Query specified join fetching, but the owner of the fetched association was not present".
I have tried with some other approaches, the most simple one that avoids doing n + 1 queries is to remove the creation of the Pojo object from your query and process the result list, manually creating the objects:
String hql = "SELECT acc, SUM(t.value)"
+ " FROM " + Transaction.class.getName() + " t"
+ " JOIN t.account acc"
+ " GROUP BY acc";
Query query = getEntityManager().createQuery(hql);
List<Pojo> pojoList = new ArrayList<>();
List<Object[]> list = query.getResultList();
for (Object[] result : list)
pojoList.add(new Pojo((Account)result[0], (BigDecimal)result[1]));
Well PostgreSQL (And any other SQL database too) will block you from using mentioned query: you have to group by all columns of account table, not by id. That is why Hibernate generates the query, grouping by ID of the account - That is what is intended to be, and then fetching the other parts. Because it cannot predict in general way, what else will be needed to be joined and grouped(!!!), and in general this could produce situation, when multiple entities with the same ID are fetched (just create a proper query and take a look at execution plan, this will be especially significant when you have OneToMany fields in your Account entity, or any other ManyToOne part of the Account entity) that is why Hibernate behaves this way.
Also, having accounts with mentioned IDs in First level cache, will force Hibernate to pick them up from that. Or IF they are rarely modified entities, you can put them in Second level cache, and hibernate will not make query to database, but rather pick them from Second level cache.
If you need to get those from database in single hint, but not use all the goodness of Hibernate, just go to pure JPA Approach based on Native queries, like this:
#NamedNativeQuery(
name = "Pojo.groupedInfo",
query = "SELECT account.*, SUM(t.value) as sum FROM transactions JOIN accounts on transactions.account_id = accounts.id GROUP BY account.id, account.etc ...",
resultClass = Pojo.class,
resultSetMapping = "Pojo.groupedInfo")
#SqlResultSetMapping(
name = "Pojo.groupedInfo",
classes = {
#ConstructorResult(
targetClass = Pojo.class,
columns = {
#ColumnResult(name = "sum", type = BigDecimal.class),
/*
* Mappings for Account part of entity.
*/
}
)
}
)
public class Pojo implements Serializable {
private BigDecimal sum;
/* .... */
public Pojo(BigDecimal sum, ...) {}
/* .... */
}
For sure this will work for you well, unless you will use the Account, fetched by this query in other entities. This will make Hibernate "mad" - the "entity", but not fetched by Hibernate...
Interesting, the described behaviour is as if t instances are returned from the actual query and t.account association in the first argument of Pojo constructor is actually navigated on t instances when marshalling results of the query (when creating Pojo instances from the result rows of the query). I am not sure if this is a bug or intended feature for constructor expressions.
But the following form of the query should work (no t.account navigation in the constructor expression, and no join fetch without the owner of the fetched association because it does not make sense to eagerly initialize something that is not actually returned from the query):
SELECT new com.test.Pojo(acc, SUM(t.value))
FROM Transaction t JOIN t.account acc
GROUP BY acc
EDIT
Very good observation by Ilya Dyoshin about the group by clause; I completely oversaw it here. To stay in the HQL world, you could simply preload all accounts with transactions before executing the query with grouping:
SELECT acc FROM Account acc
WHERE acc.id in (SELECT t.account.id FROM Transaction t)
I have a trigger that runs after updating any account and it actually just updates a field (Relationship_category_r__c) in all the related contacts after few conditions.
Condition1: If we update the account type to "Member"
Condition2: If the contact doesn't have "Member" already in the (Relationship_category_r__c) field
ACTION: Update the contact Relationship_Category_r__c field to "Member - staff"
Condition2: If we update the account type to "Member - past"
ACTION: Update all the contacts Relationship_Category_r__c field to "Member - past"
The trigger works absolutely find when the account has less than 25 to 50 contacts but it generates an error when we have an account more than 55 or so contacts
ERROR: Apex trigger UpdateAllContacts caused an unexpected exception, contact your administrator: UpdateAllContacts: System.LimitException: Too many SOQL queries: 101
======================================= TRIGGER ==============================
trigger UpdateAllContacts on Account (after update) {
for ( Account acc : Trigger.New ) {
List<Contact> listCon = [Select id, Relationship_Category_r__c from Contact where AccountId =: acc.id];
for ( Contact con : listCon ) {
if ( acc.Type=='Member' ) {
if ( con.Relationship_Category_r__c != 'Member' ) {
con.Relationship_Category_r__c = 'Member - staff';
}
} else if ( acc.Type=='Member - past ' ) {
con.Relationship_Category_r__c = 'Member - past';
}
}
try {
update listCon;
}
catch (DmlException e) {}
}
}
Any help will be greatly appreciated
Thanks
Couple of things that jump out at me here:
First and foremost is the main cause of your error: a SOQL query within a loop. You need to bulkify your trigger to perform a single query, rather than querying once for each Account record in your update batch.
You have a DML operation (update listCon;) within that same loop, which will exacerbate the problem if you happen to have any SOQL queries in your Contact triggers. This update should also be bulkified, so that you are making as few inserts/updates as possible (in this case you can limit it to a single update call).
You are updating all Contact records queried regardless of whether or not they've been updated by your code. This can lead to unnecessarily long processing times, and can easily be prevented by keeping track of which records should be updated in a second list.
This may be by design, but you're suppressing any errors in your update call without even attempting to deal with them. There are many different ways to go about this depending on your implementation so I won't delve into that, but in most circumstances you would probably want to at least be aware that your update to those records was failing so you can correct the issue.
After making a few corrections to your code we are left with the following which uses a single SOQL query, single DML statement, and won't update any Contact records that haven't been modified by the trigger:
trigger UpdateAllContacts on Account (after update) {
List<Contact> updateCons = new List<Contact>();
for ( Contact con : [select Id, AccountId, Relationship_Category_r__c from Contact where AccountId in :Trigger.NewMap.keySet()] ) {
Account parentAcc = Trigger.NewMap.get(con.AccountId);
if ( parentAcc.Type == 'Member' ) {
if ( con.Relationship_Category_r__c != 'Member' ) {
con.Relationship_Category_r__c = 'Member - staff';
updateCons.add(con);
}
} else if ( parentAcc.Type == 'Member - past ' ) {
con.Relationship_Category_r__c = 'Member - past';
updateCons.add(con);
}
}
update updateCons;
}
Using JPA, I have a list of entries from my database :
User(id, firstname, lastname, email)
That I get by doing:
List<User> users = User.find("lastname = ?", "smith");
And I'd like to update all in one request, by doing something like this :
"UPDATE USER SET email = null IN :list"
and then set the parameter "list" to users
Is it possible? if so, how?
Thanks for your help :)
Well, you could embed the query that you used to obtain list in the where clause of the update.
UPDATE User a SET a.email = null
WHERE user IN (SELECT b FROM User b WHERE lastName = :?)
By doing this you'd be doing the query to search the list and the update in single update query.
How do you like that? Do you think this could work?
-EDIT-
Since you want to use the original list of items instead of a list just retrieved from the database, you can still ensure you build the original list like this
UPDATE User a SET a.email = null
WHERE user IN (SELECT b FROM User b WHERE lastName IN(:originalList))
Then when you invoke it, you can do something like this:
Collection<String> originalList = Arrays.asList("Kenobi", "Skywalker", "Windu");
query.setParameter("originalList", originalList);
By this, you can still ensure the query will only contain items in your original list and not any possible new item from the database, provided that that last name is a candidate key in the database, otherwise I would recommend that you use the ID for the subquery instend of the last name.
if you have jpa+hibernate you can use entityManager.createQuery() for creating hql query
like that:
String hql = "UPDATE Supplier SET name = :newName WHERE name IN :name";
entityManager.createQuery(hql);