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add joins to entity types (range variables), RIGHT JOIN, and FULL JOIN
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see #128, #466
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@gavinking
gavinking committed Aug 14, 2023
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Showing 1 changed file with 175 additions and 76 deletions.
251 changes: 175 additions & 76 deletions spec/src/main/asciidoc/ch04-query-language.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -274,14 +274,21 @@ from_clause ::=
FROM identification_variable_declaration
{, {identification_variable_declaration | collection_member_declaration}}*
identification_variable_declaration ::= range_variable_declaration {join | fetch_join}*
identification_variable_declaration ::= range_variable_declaration join*
range_variable_declaration ::= entity_name [AS] identification_variable
join ::= join_spec join_association_path_expression [AS] identification_variable [join_condition]
join ::= range_join | path_join | fetch_join
range_join ::= join_spec range_variable_declaration [join_condition]
path_join ::=
join_spec join_association_path_expression [AS] identification_variable [join_condition]
fetch_join ::= join_spec FETCH join_association_path_expression
join_spec ::= [INNER | LEFT [OUTER] | RIGHT [OUTER] | FULL [OUTER]] JOIN
join_association_path_expression ::=
join_collection_valued_path_expression |
join_single_valued_path_expression |
Expand All @@ -292,8 +299,6 @@ join_collection_valued_path_expression ::= identification_variable.{single_value
join_single_valued_path_expression ::= identification_variable.{single_valued_embeddable_object_field.}*single_valued_object_field
join_spec ::= [LEFT [OUTER] | INNER] JOIN
join_condition ::= ON conditional_expression
collection_member_declaration ::= IN (collection_valued_path_expression) [AS] identification_variable
Expand Down Expand Up @@ -409,7 +414,7 @@ query (or subquery) in which it is defined and is also visible to any
subqueries within that query scope that do not define an identification
variable of the same name.

==== Range Variable Declarations
==== Range Variable Declarations [[a4766]]

The syntax for declaring an
identification variable as a range variable is similar to that of SQL;
Expand Down Expand Up @@ -657,22 +662,41 @@ SELECT DISTINCT l.product
FROM Order AS o JOIN o.lineItems l
----

It is illegal to use a
_collection_valued_path_expression_ other than in the FROM clause of a
query except in an _empty_collection_comparison_expression,_ in a
_collection_member_expression_, or as an argument to the SIZE operator.
A _collection_valued_path_expression_ may only occur in:

- the FROM clause of a query,
- an _empty_collection_comparison_expression,_
- a _collection_member_expression_, or
- as an argument to the SIZE operator.

See <<a5139>>, <<a5150>>, and <<a5284>>.

==== Joins

An inner join may be implicitly specified by
the use of a cartesian product in the FROM clause and a join condition
in the WHERE clause. In the absence of a join condition, this reduces to
the cartesian product.
JPQL defines the following varieties of join:

- inner joins,
- left outer joins,
- right outer joins,
- full outer joins.

The main use case for this generalized style
of join is when a join condition does not involve a foreign key
relationship that is mapped to an entity relationship.
The semantics of each variety of join is identical to SQL, and the
syntax is borrowed from ANSI SQL.

Every join has a target, either:

- an entity-valued path expression, or
- an entity type (that is, range variable declaration, as already
specified in <<a4766>>).

An inner join may be implicitly specified by the use of a cartesian
product in the FROM clause and a join condition in the WHERE clause.
In the absence of a join condition, this reduces to the cartesian
product.

The main use case for this generalized style of join is when a join
condition does not involve a foreign key relationship mapped to an
association between entities.

Example:

Expand All @@ -681,18 +705,23 @@ Example:
SELECT c FROM Customer c, Employee e WHERE c.hatsize = e.shoesize
----

In general, use of this style of inner join
(also referred to as theta-join) is less typical than explicitly defined
joins over relationships.
This style of inner join (sometimes called a "theta" join) is less
typical than explicitly defined joins over relationships.

The syntax for explicit join operations is as
follows:
The syntax for explicit join operations is given by:

----
join ::= join_spec join_association_path_expression [AS] identification_variable [join_condition]
join ::= range_join | path_join | fetch_join
range_join ::= join_spec range_variable_declaration [join_condition]
path_join ::=
join_spec join_association_path_expression [AS] identification_variable [join_condition]
fetch_join ::= join_spec FETCH join_association_path_expression
join_spec ::= [INNER | LEFT [OUTER] | RIGHT [OUTER] | FULL [OUTER]] JOIN
join_association_path_expression ::=
join_collection_valued_path_expression |
join_single_valued_path_expression |
Expand All @@ -705,51 +734,93 @@ join_collection_valued_path_expression ::=
join_single_valued_path_expression ::=
identification_variable.{single_valued_embeddable_object_field.}*single_valued_object_field
join_spec ::= [LEFT [OUTER] | INNER] JOIN
join_condition ::= ON conditional_expression
----

The inner and outer join operation types
described in <<a4884>>, <<a4898>>, and <<a4931>> are supported.
The inner and outer join operation types described in <<a4884>>, <<a4898>>,
and <<a4931>> are supported.

===== Inner Joins [[a4884]]

The syntax for an inner join to an entity type is given by:

----
[INNER] JOIN range_variable_declaration [join_condition]
----

The keyword INNER is optional and does not affect the semantics
of the query.

[source,sql]
----
SELECT c
FROM Customer c
JOIN Order o ON o.customer.id = c.id
WHERE c.status = 1
----

Or, equivalently:

[source,sql]
----
SELECT c
FROM Customer c
INNER JOIN Order o ON o.customer.id = c.id
WHERE c.status = 1
----

These queries are equivalent to the following query involving
an implicit "theta" join:

===== Inner Joins (Relationship Joins) [[a4884]]
[source,sql]
----
SELECT c
FROM Customer c, Order o
WHERE o.customer.id = c.id AND c.status = 1
----

The syntax for the inner join operation is
The syntax for an inner join over an association is given by:

----
[INNER] JOIN join_association_path_expression [AS] identification_variable [join_condition]
----

For example, the query below joins over the
relationship between customers and orders. This type of join typically
equates to a join over a foreign key relationship in the database.
For example, the query below joins over the relationship between
customers and orders. This type of join typically equates to a
join over a foreign key relationship in the database.

[source,sql]
----
SELECT c FROM Customer c JOIN c.orders o WHERE c.status = 1
SELECT c
FROM Customer c
JOIN c.orders o
WHERE c.status = 1
----

The keyword INNER may optionally be used:
Equivalently:

[source,sql]
----
SELECT c FROM Customer c INNER JOIN c.orders o WHERE c.status = 1
SELECT c
FROM Customer c
INNER JOIN c.orders o
WHERE c.status = 1
----

This is equivalent to the following query
using the earlier IN construct, defined in
<<a19497>>. It selects those customers of
This is equivalent to the following query using the earlier IN
construct, defined in <<a19497>>. It selects those customers of
status 1 for which at least one order exists:

[source,sql]
----
SELECT OBJECT(c) FROM Customer c, IN(c.orders) o WHERE c.status = 1
SELECT OBJECT(c)
FROM Customer c, IN(c.orders) o
WHERE c.status = 1
----

The query below joins over _Employee_,
_ContactInfo_ and _Phone_. _ContactInfo_ is an embeddable class that
consists of an address and set of phones. _Phone_ is an entity.
The query below joins over _Employee_, _ContactInfo_ and _Phone_.
_ContactInfo_ is an embeddable class that consists of an address
and set of phones. _Phone_ is an entity.

[source,sql]
----
Expand All @@ -758,27 +829,53 @@ FROM Employee e JOIN e.contactInfo c JOIN c.phones p
WHERE c.address.zipcode = '95054'
----

A join condition may be specified for an
inner join. This is equivalent to specification of the same condition in
the WHERE clause.
A join condition may be specified for an inner join. This is equivalent
to specification of the same condition in the WHERE clause.

===== Left Outer Joins [[a4898]]
===== Outer Joins [[a4898]]

LEFT JOIN and LEFT OUTER JOIN are synonymous.
They enable the retrieval of a set of entities where matching values in
the join condition may be absent.
The syntax for an outer join to an entity type is given by:

The syntax for a left outer join is
----
{LEFT|RIGHT|FULL} [OUTER] JOIN range_variable_declaration
----

The keyword OUTER is optional and does not affect the semantics of
the query.

[source,sql]
----
LEFT [OUTER] JOIN join_association_path_expression [AS] identification_variable [join_condition]
SELECT c
FROM Customer c
LEFT JOIN Order o ON o.customer.id = c.id
WHERE c.status = 1
----

Or, equivalently:

[source,sql]
----
SELECT c
FROM Customer c
LEFT OUTER JOIN Order o ON o.customer.id = c.id
WHERE c.status = 1
----

Outer joins enable the retrieval of a set of entities where matching
values in the join condition may be absent. For example, the queries
above return _Customer_ instances with no matching _Order_.

The syntax for an outer join over an association is given by:

----
{LEFT|RIGHT|FULL} [OUTER] JOIN join_association_path_expression [AS] identification_variable [join_condition]
----

An outer join without a specified join
condition has an implicit join condition over the foreign key
relationship corresponding to the join_association_path_expression. It
would typically be mapped to a SQL outer join with an ON condition on
the foreign key relationship as in the queries below:
An association outer join without no explicit _join_condition_ has an
implicit join condition inferred from the foreign key relationship
mapped by the _join_association_path_expression_. Typically, a JPQL
join of this form is translated to a SQL outer join with an ON condition
specifying the foreign key relationship, as in the following examples.

Jakarta Persistence query language:

Expand All @@ -799,9 +896,9 @@ FROM Suppliers s LEFT JOIN Products p
GROUP By s.name
----

An outer join with an explicit ON condition
would cause an additional specified join condition to be added to the
generated SQL:
An explicit _join_condition_ (that is, an ON condition in the JOIN)
results in an additional restriction in the ON condition of the
generated SQL.

Jakarta Persistence query language:

Expand All @@ -823,8 +920,8 @@ FROM Suppliers s LEFT JOIN Products p
GROUP BY s.name
----

Note that the result of this query will be
different from that of the following query:
Note that the result of this query will be different from that of the
following query:

[source,sql]
----
Expand All @@ -834,27 +931,27 @@ WHERE p.status = 'inStock'
GROUP BY s.name
----

The result of the latter query will exclude
suppliers who have no products in stock whereas the former query will
include them.
The result of the latter query will exclude suppliers who have no
products in stock whereas the former query will include them.

An important use case for LEFT JOIN is in
enabling the prefetching of related data items as a side effect of a
query. This is accomplished by specifying the LEFT JOIN as a FETCH JOIN
as described below.
An important use case for LEFT JOIN is in enabling the prefetching of
related data items as a side effect of a query. This is accomplished by
specifying the LEFT JOIN as a FETCH JOIN, as described below.

===== Fetch Joins [[a4931]]

A FETCH JOIN enables the fetching of an
association or element collection as a side effect of the execution of a
query.
A FETCH JOIN clause in a query results in eager fetching of an association
or element collection as a side effect of execution of the query.

The syntax for a fetch join is
The syntax for a fetch join is given by:

----
fetch_join ::= [LEFT [OUTER] | INNER] JOIN FETCH join_association_path_expression
----

A FETCH JOIN must be an INNER or LEFT (OUTER) join. A FETCH JOIN does not
have an explicit join condition or identification variable.

The association referenced by the right side
of the FETCH JOIN clause must be an association or element collection
that is referenced from an entity or embeddable that is returned as a
Expand Down Expand Up @@ -891,7 +988,7 @@ the FROM clause of a subquery.
==== Collection Member Declarations

An identification variable declared by a
collection_member_declaration ranges over values of a collection
_collection_member_declaration_ ranges over values of a collection
obtained by navigation using a path expression.

An identification variable of a collection
Expand Down Expand Up @@ -2956,12 +3053,14 @@ delete_statement ::= delete_clause [where_clause]
from_clause ::=
FROM identification_variable_declaration
{, {identification_variable_declaration | collection_member_declaration}}*
identification_variable_declaration ::= range_variable_declaration {join | fetch_join}*
identification_variable_declaration ::= range_variable_declaration join*
range_variable_declaration ::= entity_name [AS] identification_variable
join ::= join_spec join_association_path_expression [AS] identification_variable
[join_condition]
join ::= range_join | path_join | fetch_join
range_join ::= join_spec range_variable_declaration
path_join ::=
join_spec join_association_path_expression [AS] identification_variable [join_condition]
fetch_join ::= join_spec FETCH join_association_path_expression
join_spec ::= [LEFT [OUTER] | INNER] JOIN
join_spec ::= [INNER | LEFT [OUTER] | RIGHT [OUTER] | FULL [OUTER]] JOIN
join_condition ::= ON conditional_expression
join_association_path_expression ::=
join_collection_valued_path_expression |
Expand Down

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