How can I create a SELECT EXISTS (subquery) with jOOQ? - sql

I want to build and execute a query like this with jOOQ.
SELECT EXISTS( subquery )
For exemple:
SELECT EXISTS(SELECT 1 FROM icona_etiqueta WHERE pvp IS NULL AND unitat_venda = 'GRAMS')
How can I do it? Can it be done?

Found it. I was looking for a selectExists method and got confused by the DSL.exists() predicate constructor.
There is a much more convenient fetchExists(subquery).
My specific example is resolved like this:
create.fetchExists(
create.selectOne()
.from(ICONA_ETIQUETA)
.where(ICONA_ETIQUETA.PVP.isNull(),
ICONA_ETIQUETA.UNITAT_VENDA.eq('GRAMS'))
);
Which directly returns a boolean.

Your own solution is the most convenient approach to what you want to be doing. A more general approach is to use:
create.select(field(exists(...)));
Where you wrap a Condition (created by DSL.exists(Select)) in a Field using DSL.field(Condition). As of jOOQ 3.9, Field<Boolean> and Condition are not the same types. This has changed in the jOOQ 3.17 with #11969. You can now also just write:
create.select(exists(...));

Related

Check existence of given text in a table

I have a course code name COMP2221.
I also have a function finder(int) that can find all codes matching a certain pattern.
Like:
select * from finder(20004)
will give:
comp2211
comp2311
comp2411
comp2221
which match the pattern comp2###.
My question is how to express "whether comp2221 is in finder(20004)" in a neat way?
How to express "whether comp2221 is in finder(20004)" in a neat way?
Use an EXISTS expression and put the test into the WHERE clause:
SELECT EXISTS (SELECT FROM finder(20004) AS t(code) WHERE code = 'comp2221');
Returns a single TRUE or FALSE. Never NULL and never more than one row - even if your table function finder() returns duplicates.
Or fork the function finder() to integrate the test directly. Probably faster.

Handle null values within SQL IN clause

I have following sql query in my hbm file. The SCHEMA, A and B are schema and two tables.
select
*
from SCHEMA.A os
inner join SCHEMA.B o
on o.ORGANIZATION_ID = os.ORGANIZATION_ID
where
case
when (:pass = 'N' and os.ORG_ID in (:orgIdList)) then 1
when (:pass = 'Y') then 1
end = 1
and (os.ORG_SYNONYM like :orgSynonym or :orgSynonym is null)
This is a pretty simple query. I had to use the case - when to handle the null value of "orgIdList" parameter(when null is passed to sql IN it gives error). Below is the relevant java code which sets the parameter.
if (_orgSynonym.getOrgIdList().isEmpty()) {
query.setString("orgIdList", "pass");
query.setString("pass", "Y");
} else {
query.setString("pass", "N");
query.setParameterList("orgIdList", _orgSynonym.getOrgIdList());
}
This works and give me the expected output. But I would like to know if there is a better way to handle this situation(orgIdList sometimes become null).
There must be at least one element in the comma separated list that defines the set of values for the IN expression.
In other words, regardless of Hibernate's ability to parse the query and to pass an IN(), regardless of the support of this syntax by particular databases (PosgreSQL doesn't according to the Jira issue), Best practice is use a dynamic query here if you want your code to be portable (and I usually prefer to use the Criteria API for dynamic queries).
If not need some other work around like what you have done.
or wrap the list from custom list et.

Liferay DynamicQuery - xPath and Array comparison

My final goal is I want to get plid and portletId that can be display my article(or entry with any type if it is possible).
I have sql query that return me any portlet availble for display my article.
But when I have to use dynamicQuery to get the same results, I get problem with xPath and array comparison, please help!
SELECT * FROM portletpreferences pr
WHERE pr.preferences != '<portlet-preferences />' AND pr.ownerid = 0 AND pr.portletid ilike '%_INSTANCE_%' AND pr.plid IN(
SELECT layout.plid FROM layout
WHERE layout.type_ = 'portlet' AND layout.groupid = 19 AND layout.hidden_ is false)
AND pr.portletpreferencesid IN (
SELECT pr.portletpreferencesid FROM portletpreferences pr
WHERE 'true' = ANY(xpath('//preference[name="anyAssetType"]/value/text()', XMLPARSE(DOCUMENT pr.preferences))::text[])
OR (SELECT (array(SELECT id_ FROM journalstructure))::text[]) && xpath('//preference[name="classTypeIds"]/value/text()', XMLPARSE(DOCUMENT pr.preferences))::text[] )
If you are bent upon using this same query, then use this query directly with Custom-SQL in liferay by creating custom-finders instead of using DynamicQuery. That would give you a lot of flexibility in using any type of SQL query directly.
I don't think this query can be converted to DynamicQuery, but if you do manage to convert it then please do post it here :-)
DynamicQuery is very powerful, see e.g. my answer how to find layouts with specific JournalArticles. I think your requirement is similar to this one:
Liferay: How to find all Layouts with the specific JournalArticle in AssetPublisher portlets?

Django select only rows with duplicate field values

suppose we have a model in django defined as follows:
class Literal:
name = models.CharField(...)
...
Name field is not unique, and thus can have duplicate values. I need to accomplish the following task:
Select all rows from the model that have at least one duplicate value of the name field.
I know how to do it using plain SQL (may be not the best solution):
select * from literal where name IN (
select name from literal group by name having count((name)) > 1
);
So, is it possible to select this using django ORM? Or better SQL solution?
Try:
from django.db.models import Count
Literal.objects.values('name')
.annotate(Count('id'))
.order_by()
.filter(id__count__gt=1)
This is as close as you can get with Django. The problem is that this will return a ValuesQuerySet with only name and count. However, you can then use this to construct a regular QuerySet by feeding it back into another query:
dupes = Literal.objects.values('name')
.annotate(Count('id'))
.order_by()
.filter(id__count__gt=1)
Literal.objects.filter(name__in=[item['name'] for item in dupes])
This was rejected as an edit. So here it is as a better answer
dups = (
Literal.objects.values('name')
.annotate(count=Count('id'))
.values('name')
.order_by()
.filter(count__gt=1)
)
This will return a ValuesQuerySet with all of the duplicate names. However, you can then use this to construct a regular QuerySet by feeding it back into another query. The django ORM is smart enough to combine these into a single query:
Literal.objects.filter(name__in=dups)
The extra call to .values('name') after the annotate call looks a little strange. Without this, the subquery fails. The extra values tricks the ORM into only selecting the name column for the subquery.
try using aggregation
Literal.objects.values('name').annotate(name_count=Count('name')).exclude(name_count=1)
In case you use PostgreSQL, you can do something like this:
from django.contrib.postgres.aggregates import ArrayAgg
from django.db.models import Func, Value
duplicate_ids = (Literal.objects.values('name')
.annotate(ids=ArrayAgg('id'))
.annotate(c=Func('ids', Value(1), function='array_length'))
.filter(c__gt=1)
.annotate(ids=Func('ids', function='unnest'))
.values_list('ids', flat=True))
It results in this rather simple SQL query:
SELECT unnest(ARRAY_AGG("app_literal"."id")) AS "ids"
FROM "app_literal"
GROUP BY "app_literal"."name"
HAVING array_length(ARRAY_AGG("app_literal"."id"), 1) > 1
Ok, so for some reason none of the above worked for, it always returned <MultilingualQuerySet []>. I use the following, much easier to understand but not so elegant solution:
dupes = []
uniques = []
dupes_query = MyModel.objects.values_list('field', flat=True)
for dupe in set(dupes_query):
if not dupe in uniques:
uniques.append(dupe)
else:
dupes.append(dupe)
print(set(dupes))
If you want to result only names list but not objects, you can use the following query
repeated_names = Literal.objects.values('name').annotate(Count('id')).order_by().filter(id__count__gt=1).values_list('name', flat='true')

How to select if a row exists in HQL

EDIT: Specifically talking about querying against no table. Yes I can use exists, but I'd have to do
select case when exists (blah) then 1 else 0 end as conditionTrue
from ARealTableReturningMultipleRows
In T-SQL I can do:
select case when exists(blah) then 1 else 0 end as conditionTrue
In Oracle I can do:
select case when exists(blah) then 1 else 0 end as conditionTrue from DUAL
How can I achieve the same thing in HQL?
select count() seems like the second-best alternative, but I don't want to have to process every row in the table if I don't need to.
Short answer: I believe it's NOT possible.
My reasoning:
According to Where can I find a list of all HQL keywords? Hibernate project doesn't publish HQL grammar on their website, it's available in the Hibernate full distribution as a .g ANTLR file though.
I don't have much experience with .g files from ANTLR, but you can find this in the file (hibernate-distribution-3.6.1.Final/project/core/src/main/antlr/hql.g):
selectFrom!
: (s:selectClause)? (f:fromClause)? {
// If there was no FROM clause and this is a filter query, create a from clause. Otherwise, throw
// an exception because non-filter queries must have a FROM clause.
if (#f == null) {
if (filter) {
#f = #([FROM,"{filter-implied FROM}"]);
}
else
throw new SemanticException("FROM expected (non-filter queries must contain a FROM clause)");
}
which clearly states there are some HQL queries having no FROM clause, but that's acceptable if that's a filter query. Now again, I am not an expert in HQL/Hibernate, but I believe a filter query is not a full query but something you define using session.createFilter (see How do I turn item ordering HQL into a filter query?), so that makes me think there's no way to omit the FROM clause.
I'm use fake table with one row for example MyDual.
select case when exists(blah) then 1 else 0 end as conditionTrue from MyDual
According to http://docs.jboss.org/hibernate/core/3.3/reference/en/html/queryhql.html#queryhql-expressions it looks like they support both case and exists statements.