14.10. Expressions
Expressions used in the
where clause include the following:
- mathematical operators:
+, -, *, / - binary comparison operators:
=, >=, <=, <>, !=, like - logical operations
and, or, not - Parentheses
( )that indicates grouping in,not in,between,is null,is not null,is empty,is not empty,member ofandnot member of- "Simple" case,
case ... when ... then ... else ... end, and "searched" case,case when ... then ... else ... end - string concatenation
...||...orconcat(...,...) current_date(),current_time(), andcurrent_timestamp()second(...),minute(...),hour(...),day(...),month(...), andyear(...)- Any function or operator defined by EJB-QL 3.0:
substring(), trim(), lower(), upper(), length(), locate(), abs(), sqrt(), bit_length(), mod() coalesce()andnullif()str()for converting numeric or temporal values to a readable stringcast(... as ...), where the second argument is the name of a Hibernate type, andextract(... from ...)if ANSIcast()andextract()is supported by the underlying database- the HQL
index()function, that applies to aliases of a joined indexed collection - HQL functions that take collection-valued path expressions:
size(), minelement(), maxelement(), minindex(), maxindex(), along with the specialelements()andindicesfunctions that can be quantified usingsome, all, exists, any, in. - Any database-supported SQL scalar function like
sign(),trunc(),rtrim(), andsin() - JDBC-style positional parameters
? - named parameters
:name,:start_date, and:x1 - SQL literals
'foo',69,6.66E+2,'1970-01-01 10:00:01.0' - Java
public static finalconstantseg.Color.TABBY
in and between can be used as follows:
from DomesticCat cat where cat.name between 'A' and 'B'
from DomesticCat cat where cat.name in ( 'Foo', 'Bar', 'Baz' )
The negated forms can be written as follows:
from DomesticCat cat where cat.name not between 'A' and 'B'
from DomesticCat cat where cat.name not in ( 'Foo', 'Bar', 'Baz' )
Similarly,
is null and is not null can be used to test for null values.
Booleans can be easily used in expressions by declaring HQL query substitutions in Hibernate configuration:
<property name="hibernate.query.substitutions">true 1, false 0</property>
This will replace the keywords
true and false with the literals 1 and 0 in the translated SQL from this HQL:
from Cat cat where cat.alive = true
You can test the size of a collection with the special property
size or the special size() function.
from Cat cat where cat.kittens.size > 0
from Cat cat where size(cat.kittens) > 0
For indexed collections, you can refer to the minimum and maximum indices using
minindex and maxindex functions. Similarly, you can refer to the minimum and maximum elements of a collection of basic type using the minelement and maxelement functions. For example:
from Calendar cal where maxelement(cal.holidays) > current_date
from Order order where maxindex(order.items) > 100
from Order order where minelement(order.items) > 10000
The SQL functions
any, some, all, exists, in are supported when passed the element or index set of a collection (elements and indices functions) or the result of a subquery (see below):
select mother from Cat as mother, Cat as kit where kit in elements(foo.kittens)
select p from NameList list, Person p where p.name = some elements(list.names)
from Cat cat where exists elements(cat.kittens)
from Player p where 3 > all elements(p.scores)
from Show show where 'fizard' in indices(show.acts)
Note that these constructs -
size, elements, indices, minindex, maxindex, minelement, maxelement - can only be used in the where clause in Hibernate3.
Elements of indexed collections (arrays, lists, and maps) can be referred to by index in a where clause only:
from Order order where order.items[0].id = 1234
select person from Person person, Calendar calendar
where calendar.holidays['national day'] = person.birthDay
and person.nationality.calendar = calendarselect item from Item item, Order order where order.items[ order.deliveredItemIndices[0] ] = item and order.id = 11
select item from Item item, Order order where order.items[ maxindex(order.items) ] = item and order.id = 11
The expression inside
[] can even be an arithmetic expression:
select item from Item item, Order order where order.items[ size(order.items) - 1 ] = item
HQL also provides the built-in
index() function for elements of a one-to-many association or collection of values.
select item, index(item) from Order order
join order.items item
where index(item) < 5
Scalar SQL functions supported by the underlying database can be used:
from DomesticCat cat where upper(cat.name) like 'FRI%'
Consider how much longer and less readable the following query would be in SQL:
select cust
from Product prod,
Store store
inner join store.customers cust
where prod.name = 'widget'
and store.location.name in ( 'Melbourne', 'Sydney' )
and prod = all elements(cust.currentOrder.lineItems)
Hint: something like
SELECT cust.name, cust.address, cust.phone, cust.id, cust.current_order
FROM customers cust,
stores store,
locations loc,
store_customers sc,
product prod
WHERE prod.name = 'widget'
AND store.loc_id = loc.id
AND loc.name IN ( 'Melbourne', 'Sydney' )
AND sc.store_id = store.id
AND sc.cust_id = cust.id
AND prod.id = ALL(
SELECT item.prod_id
FROM line_items item, orders o
WHERE item.order_id = o.id
AND cust.current_order = o.id
)