15.6. The select clause

The select clause picks which objects and properties to return in the query result set. Consider the following:

select mate
from Cat as cat
    inner join cat.mate as mate

select mate
from Cat as cat
    inner join cat.mate as mate

Copy to Clipboard

Toggle word wrap

The query will select mates of other Cats. You can express this query more compactly as:

select cat.mate from Cat cat

select cat.mate from Cat cat

Copy to Clipboard

Toggle word wrap

Queries can return properties of any value type including properties of component type:

select cat.name from DomesticCat cat
where cat.name like 'fri%'

select cat.name from DomesticCat cat
where cat.name like 'fri%'

Copy to Clipboard

Toggle word wrap

select cust.name.firstName from Customer as cust

select cust.name.firstName from Customer as cust

Copy to Clipboard

Toggle word wrap

Queries can return multiple objects and/or properties as an array of type Object[]:

select mother, offspr, mate.name
from DomesticCat as mother
    inner join mother.mate as mate
    left outer join mother.kittens as offspr

select mother, offspr, mate.name
from DomesticCat as mother
    inner join mother.mate as mate
    left outer join mother.kittens as offspr

Copy to Clipboard

Toggle word wrap

Or as a List:

select new list(mother, offspr, mate.name)
from DomesticCat as mother
    inner join mother.mate as mate
    left outer join mother.kittens as offspr

select new list(mother, offspr, mate.name)
from DomesticCat as mother
    inner join mother.mate as mate
    left outer join mother.kittens as offspr

Copy to Clipboard

Toggle word wrap

Or - assuming that the class Family has an appropriate constructor - as an actual typesafe Java object:

select new Family(mother, mate, offspr)
from DomesticCat as mother
    join mother.mate as mate
    left join mother.kittens as offspr

select new Family(mother, mate, offspr)
from DomesticCat as mother
    join mother.mate as mate
    left join mother.kittens as offspr

Copy to Clipboard

Toggle word wrap

You can assign aliases to selected expressions using as:

select max(bodyWeight) as max, min(bodyWeight) as min, count(*) as n
from Cat cat

select max(bodyWeight) as max, min(bodyWeight) as min, count(*) as n
from Cat cat

Copy to Clipboard

Toggle word wrap

This is most useful when used together with select new map:

select new map( max(bodyWeight) as max, min(bodyWeight) as min, count(*) as n )
from Cat cat

select new map( max(bodyWeight) as max, min(bodyWeight) as min, count(*) as n )
from Cat cat

Copy to Clipboard

Toggle word wrap

This query returns a Map from aliases to selected values.

Nach oben