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Same here for MySQL 5.5.40. In the generated SQL only the topmost entity was quoted and its simple class name was used (because it is abstract and have no discriminator value).

I tried to remove @DiscriminatorColumn and @DiscriminatorValue annotations but got even more cryptic exception without actual SQL:

Caused by: java.lang.IllegalArgumentException: Parameter value [PurchaseTransaction] did not match expected type [java.lang.Integer (n/a)]
	at org.hibernate.jpa.spi.BaseQueryImpl.validateBinding(BaseQueryImpl.java:874) ~[BaseQueryImpl.class:4.3.7.Final]
	at org.hibernate.jpa.internal.QueryImpl.access$000(QueryImpl.java:80) ~[QueryImpl.class:4.3.7.Final]
	at org.hibernate.jpa.internal.QueryImpl$ParameterRegistrationImpl.bindValue(QueryImpl.java:248) ~[QueryImpl$ParameterRegistrationImpl.class:4.3.7.Final]
	at org.hibernate.jpa.internal.QueryImpl$JpaPositionalParameterRegistrationImpl.bindValue(QueryImpl.java:337) ~[QueryImpl$JpaPositionalParameterRegistrationImpl.class:4.3.7.Final]
	at org.hibernate.jpa.spi.BaseQueryImpl.setParameter(BaseQueryImpl.java:674) ~[BaseQueryImpl.class:4.3.7.Final]
	at org.hibernate.jpa.spi.AbstractQueryImpl.setParameter(AbstractQueryImpl.java:198) ~[AbstractQueryImpl.class:4.3.7.Final]
	at org.hibernate.jpa.spi.AbstractQueryImpl.setParameter(AbstractQueryImpl.java:49) ~[AbstractQueryImpl.class:4.3.7.Final]

Sad that such a basic feature is broken in the Hibernate, the most used JPA implementation.