Hi Dain,
Be aware that MySQL doesn't support nested queries.
Outer joins is more portable solution IMHO.
BTW in Castor JDO we have "database drivers", which map OUTER JOINs
and FOR UPDATE to all popular databases.
Oleg
Dain Sundstrom wrote:
> Issue 2: IS EMPTY function. How should I map the following ejb-ql query:
> SELECT OBJECT(o)
> FROM Order o
> WHERE o.lineItems IS EMPTY
> Solution A:
> SELECT o.ordernumber
> FROM Order o
> WHERE NOT EXISTS (
> SELECT l.pk
> FROM Order o, LineItem l
> WHERE o.ordernumber = l.ordernumber)
> I like this because it does not use an outer join (thanks Dave Smith). Does
> it have performance problems?
> Solution B:
> SELECT o.ordernumber
> FROM Order o LEFT OUTER JOIN LineItem l ON o.ordernumber = l.ordernumber
> WHERE l.ordernumber IS NULL
> This would be a major pain to map to all vendors.
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