Major Description
INNER JOIN FETCH should not generate SQL LEFT join.
Example:
lineitems (ToMany, FetchType=LAZY)
Order <===================================> OrderItem
order (ToOne, FetchType=LAZY)
For Query: select o from Order left join fetch o.lineitems
SQL generated
for DB2:
SELECT t0.oid, t0.version, t0.amount, t0.delivered, t1.ORDER_OID, t1.lid, t1.version, t1.cost, t1.quantity
FROM TORDER t0 LEFT OUTER JOIN TORDERITEM t1 ON t0.oid = t1.ORDER_OID ORDER BY t1.ORDER_OID ASC
for Oracle:
SELECT t0.oid, t0.version, t0.amount, t0.delivered, t1.ORDER_OID, t1.lid, t1.version, t1.cost, t1.quantity FROM TORDER t0, TORDERITEM t1 WHERE t0.oid = t1.ORDER_OID
ORDER BY t1.ORDER_OID ASC
The above SQL pushdown looked good.
However, if left join fetch is changed to inner join fetch:
select o from Order o inner join fetch o.lineitems
We are generating extra redundant LEFT joins:
for DB2:
SELECT t0.oid, t0.version, t0.amount, t0.delivered, t2.ORDER_OID, t2.lid, t2.version, t2.cost, t2.quantity
FROM TORDER t0 INNER JOIN TORDERITEM t1 ON t0.oid = t1.ORDER_OID LEFT OUTER JOIN TORDERITEM t2 ON t0.oid = t2.ORDER_OID ORDER BY t2.ORDER_OID ASC
for Oracle:
SELECT t0.oid, t0.version, t0.amount, t0.delivered, t2.ORDER_OID, t2.lid, t2.version, t2.cost, t2.quantity FROM TORDER t0, TORDERITEM t1, TORDERITEM t2 WHERE t0.oid = t1.ORDER_OID AND t0.oid = t2.ORDER_OID ORDER BY t2.ORDER_OID ASC
Why do we generate the extra LEFT joins even for quereis explicitly requesting INNER join fetch ?