I want to search in 16 different tables, but I don't wanna repeat the "select from DB" 16 times; I think that's not really help in performance!!!
I am using:
query="SELECT * FROM table1, table2,..., table16 WHERE id=?";
Is it correct ??
my problem is how to separate between data of tables ??
also maybe I can get from one table two or more results for one "id"; So I want to know which data is from which table !!
.
Best regards,
Your query will not work, because you are trying to join those multiple tables, whereas what you want to do is search (filter) those 16 tables.
You could use a union all to do this in a single query:
select xxx, 'table1' as source_table
from table1
where id = ?
union all
select xxx, 'table2' as source_table
from table2
where id = ?
and so on. The second derived field source_table can be used to determine which table returned which result.
You have to list all fields using aliases for fields with same name, and prefix with table names.
For example :
query = "SELECT table1.id as id_1, table2.id as id_2, ... WHERE id_1 = 23"
Probably a very long query to write, but you have solution to generate and paste it : You can do this for example with FlySpeed SqlQuery (free for personal use)
FlySpeed SqlQuery will generate all aliases for you, and automatically prefix with table names.
A little clarification would help. If all 16 tables have the same fields and you want them in a continuous list, you can use UNION as suggested above. On the other hand, if there are only a few fields that match and you want to compare the values for each table side-by-side, you'll want to use joins and provide aliases with the table names, as also suggested above.
However, looking at the snippet of code you've provided, I'm going to guess that you're either building some kind of stored procedure or else implementing SQL in some other language. If that's the case, how about loading your table names into an array and using a for loop to build the query, such as the following psuedo-code:
tableList = ["table1", "table2"...]
fieldnames = ["field1", "field2"...]
query = "SELECT "
for i = 0 to count(tableList):
for j = 0 to count(fieldnames):
query = query + tablelist[i] + "." + fieldnames[j] + ", "
j++
i++
query = query + "FROM "
for i = 0 to count(tableList):
query = query + tableList[i] + ", "
i++
query = query + "WHERE " ...
And so forth. Much of this depends on what exactly you're looking to do, how often you're looking to do it, and how often the variables (like which tables or fields you're using) are going to change.
I have been working with Oracle and Postgre and recently switched to MS SQL 2012.
I use hibernate in my application and wherever I have used the Order by Criteria:
(criteria.addOrder(Order.asc("applicationId")));
It causes an error saying:
aggregate functions dont work.
Once I comment that line out my program works and data can be retrieved.
I'm using Hibernate 3.
Is there any way to order it through hibernate without this error?
edit..
This is one error I get,
Column "SKY.tcrent.RENTNO" is invalid in the ORDER BY clause because
it is not contained in either an aggregate function or the GROUP BY
clause.
Edit 2..
MY query
Query tcSchaduleQ = getSession().createQuery("SELECT SUM(tcs.dueAmount) FROM TrialCalculationSchedule tcs WHERE tcs.facilityId=:facilityId AND tcs.rentalNumber>:rentalNumber AND tcs.dueDate>:dueDate AND dueTypeId IN(:dueTypeId) ORDER BY tcs.rentalNumber ").setInteger("rentalNumber", facility.getPeriod() - noOfprePayments).setInteger("facilityId",facility.getFacilityId()).setDate("dueDate", date).setParameterList("dueTypeId", plist);
Number tcsAmt = (Number) tcSchaduleQ.uniqueResult();
and this is what hibernate generates in HQL
SELECT
SUM(tcs.dueAmount)
FROM
TrialCalculationSchedule tcs
WHERE
tcs.facilityId=:facilityId
AND tcs.rentalNumber>:rentalNumber
AND tcs.dueDate>:dueDate
AND dueTypeId IN(
:dueTypeId
)
ORDER BY
tcs.rentalNumber
and this is the SQL
select
SUM(trialcalcu0_.DUEAMT) as col_0_0_
from
SKYBANKSLFHP.tcrent trialcalcu0_
where
trialcalcu0_.FACID=?
and trialcalcu0_.RENTNO>?
and trialcalcu0_.DUEDATE>?
and (
trialcalcu0_.DUETYPEID in (
? , ?
)
)
order by
trialcalcu0_.RENTNO
Look Like you mix aggregate and non-aggregate expressions .If you are using any aggregate function like AVG() in Select query with some other non-aggregate then you must use Group By ..
Try something like this
createQuery("SELECT SUM(tcs.dueAmount) As DueAmount ...
If you are using Criteria then it should be like this
Criteria crit = sess.createCriteria(Insurance.class);
ProjectionList proList = Projections.projectionList();
proList.add(Projections.sum("investementAmount"));
crit.setProjection(proList);
List sumResult = crit.list();
If I have a group by query
Select e.field1, e.field2...
from Entity w
group by e.field1, e.field2...
How can I count the number of rows not using NativeQuery?
I need to do something like this:
select count(*) from
(Select e.field1, e.field2...
from Entity w
group by e.field1, e.field2...)
Is there any way to do with JPQL?
in oracle you can this hql
Select sum(count(*) - count(*) + 1)
from Entity e
group by e.field1, e.field2...
but dose not work in postgres
Derived tables are not supported in JPQL, so, the best way to do it is to run a native SQL query.
After all, there is a very good reason why both JPA and Hibernate offer support for SQL queries, don't you agree?
We have a use case to count no. of rows returned by actual query. I am not getting how can I get it using criteria in hibernate.
For example suppose I want to run query
select sum(TOTAL_EARNINGS) from table where column1 = 'value1' group by column2);
Along with this query result I also want to get total rows return by above query(above query may have rownum limit also but for total rows I have to ignore rownum limit).
select count(*) from (select sum(TOTAL_EARNINGS) from table
where column1 = 'value1' group by column2);
Is there any easy way of getting this data. I am fine with running separate query to get count data but I am not getting how can I write this in hibernate using criteria. I can't even see any option in SubQueries which I can use
In general with criteria you can use projections.
You can do so, if you have an entity "Your" mapped by Hibernate:
Edited:
Accordingly to your comment, you need two results, a total count and a group by results.
//the group by results...
List result1 = session.createCriteria("Your.class").setProjection(Projections.projectionList()
.add(Projections.groupProperty("column2"))
.add(Projections.sum("totalErnings"))
).list();
//the total count result
return (Integer) session.createCriteria("Your.class").add(Restrictions.eq("column1", val)).setProjection(Projections.rowCount()).uniqueResult();
What alternatives do I have to implement a union query using hibernate? I know hibernate does not support union queries at the moment, right now the only way I see to make a union is to use a view table.
The other option is to use plain jdbc, but this way I would loose all my example/criteria queries goodies, as well as the hibernate mapping validation that hibernate performs against the tables/columns.
You could use id in (select id from ...) or id in (select id from ...)
e.g. instead of non-working
from Person p where p.name="Joe"
union
from Person p join p.children c where c.name="Joe"
you could do
from Person p
where p.id in (select p1.id from Person p1 where p1.name="Joe")
or p.id in (select p2.id from Person p2 join p2.children c where c.name="Joe");
At least using MySQL, you will run into performance problems with it later, though. It's sometimes easier to do a poor man's join on two queries instead:
// use set for uniqueness
Set<Person> people = new HashSet<Person>((List<Person>) query1.list());
people.addAll((List<Person>) query2.list());
return new ArrayList<Person>(people);
It's often better to do two simple queries than one complex one.
EDIT:
to give an example, here is the EXPLAIN output of the resulting MySQL query from the subselect solution:
mysql> explain
select p.* from PERSON p
where p.id in (select p1.id from PERSON p1 where p1.name = "Joe")
or p.id in (select p2.id from PERSON p2
join CHILDREN c on p2.id = c.parent where c.name="Joe") \G
*************************** 1. row ***************************
id: 1
select_type: PRIMARY
table: a
type: ALL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: 247554
Extra: Using where
*************************** 2. row ***************************
id: 3
select_type: DEPENDENT SUBQUERY
table: NULL
type: NULL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: NULL
Extra: Impossible WHERE noticed after reading const tables
*************************** 3. row ***************************
id: 2
select_type: DEPENDENT SUBQUERY
table: a1
type: unique_subquery
possible_keys: PRIMARY,name,sortname
key: PRIMARY
key_len: 4
ref: func
rows: 1
Extra: Using where
3 rows in set (0.00 sec)
Most importantly, 1. row doesn't use any index and considers 200k+ rows. Bad! Execution of this query took 0.7s wheres both subqueries are in the milliseconds.
Use VIEW. The same classes can be mapped to different tables/views using entity name, so you won't even have much of a duplication. Being there, done that, works OK.
Plain JDBC has another hidden problem: it's unaware of Hibernate session cache, so if something got cached till the end of the transaction and not flushed from Hibernate session, JDBC query won't find it. Could be very puzzling sometimes.
I have to agree with Vladimir. I too looked into using UNION in HQL and couldn't find a way around it. The odd thing was that I could find (in the Hibernate FAQ) that UNION is unsupported, bug reports pertaining to UNION marked 'fixed', newsgroups of people saying that the statements would be truncated at UNION, and other newsgroups of people reporting it works fine...
After a day of mucking with it, I ended up porting my HQL back to plain SQL, but doing it in a View in the database would be a good option. In my case, parts of the query were dynamically generated, so I had to build the SQL in the code instead.
I have a solution for one critical scenario (for which I struggled a lot )with union in HQL .
e.g. Instead of not working :-
select i , j from A a , (select i , j from B union select i , j from C) d where a.i = d.i
OR
select i , j from A a JOIN (select i , j from B union select i , j from C) d on a.i = d.i
YOU could do in Hibernate HQL ->
Query q1 =session.createQuery(select i , j from A a JOIN B b on a.i = b.i)
List l1 = q1.list();
Query q2 = session.createQuery(select i , j from A a JOIN C b on a.i = b.i)
List l2 = q2.list();
then u can add both list ->
l1.addAll(l2);
A view is a better approach but since hql typically returns a List or Set... you can do list_1.addAll(list_2). Totally sucks compared to a union but should work.
Perhaps I had a more straight-forward problem to solve. My 'for instance' was in JPA with Hibernate as the JPA provider.
I split the three selects (two in a second case) into multiple select and combined the collections returned myself, effectively replacing a 'union all'.
Hibernate 6 added support for UNION.
So, you can now use UNION in JPQL queries like this:
List<String> topics = entityManager.createQuery("""
select c.name as name
from Category c
union
select t.name as name
from Tag t
""", String.class)
.getResultList();
And you can also also use UNION ALL if there are no duplicates to be removed:
List<String> topics = entityManager.createQuery("""
select c.name as name
from Category c
union all
select t.name as name
from Tag t
""", String.class)
.getResultList();
Besides UNION, you can also use EXCEPT and INTERSECT.
I too have been through this pain - if the query is dynamically generated (e.g. Hibernate Criteria) then I couldn't find a practical way to do it.
The good news for me was that I was only investigating union to solve a performance problem when using an 'or' in an Oracle database.
The solution Patrick posted (combining the results programmatically using a set) while ugly (especially since I wanted to do results paging as well) was adequate for me.
Here is a special case, but might inspire you to create your own work around. The goal here is to count the total number of records from two different tables where records meet a particular criteria. I believe this technique will work for any case where you need to aggregate data from across multiple tables/sources.
I have some special intermediate classes setup, so the code which calls the named query is short and sweet, but you can use whatever method you normally use in conjunction with named queries to execute your query.
QueryParms parms=new QueryParms();
parms.put("PROCDATE",PROCDATE);
Long pixelAll = ((SourceCount)Fetch.row("PIXEL_ALL",parms,logger)).getCOUNT();
As you can see here, the named query begins to look an aweful lot like a union statement:
#Entity
#NamedQueries({
#NamedQuery(
name ="PIXEL_ALL",
query = "" +
" SELECT new SourceCount(" +
" (select count(a) from PIXEL_LOG_CURR1 a " +
" where to_char(a.TIMESTAMP, 'YYYYMMDD') = :PROCDATE " +
" )," +
" (select count(b) from PIXEL_LOG_CURR2 b" +
" where to_char(b.TIMESTAMP, 'YYYYMMDD') = :PROCDATE " +
" )" +
") from Dual1" +
""
)
})
public class SourceCount {
#Id
private Long COUNT;
public SourceCount(Long COUNT1, Long COUNT2) {
this.COUNT = COUNT1+COUNT2;
}
public Long getCOUNT() {
return COUNT;
}
public void setCOUNT(Long COUNT) {
this.COUNT = COUNT;
}
}
Part of the magic here is to create a dummy table and insert one record into it. In my case, I named it dual1 because my database is Oracle, but I don't think it matters what you call the dummy table.
#Entity
#Table(name="DUAL1")
public class Dual1 {
#Id
Long ID;
}
Don't forget to insert your dummy record:
SQL> insert into dual1 values (1);
As Patrick said, appending the LISTs from each SELECT would be a good idea but remember that it acts like UNION ALL. To avoid this side effect, just control if the object is already added in final collection or not. If no, then add it.
Something else that you should care about is that if you have any JOIN in each SELECT, the result would be a list of object array(List<Object[]>) so you have to iterate over it to only keep the object that you need.
Hope it works.