When a java "double" type is defined in an entity class, a "float" type column is created in oracle database when setting hibernate.hbm2ddl.auto=create(or update).

The java "double" type is interpreted as "double precision" in the table creation script by Hibernate. For example,

a table create script could look like:

CREATE TABLE MyUser (
user_id NUMBER(9) PRIMARY KEY,
height double precision NOT NULL)

It generates a column "height" of type "float".

The same table creation script generates type "double" in mysql database.

It appears that oracle database doesn't have a data type "double". It has "BINARY_DOUBLE" instead.

In addition, after a double type being created as "float" in the database, if setting the hibernate.hbm2ddl.auto=validate, it throws error:

Caused by: org.hibernate.HibernateException: Wrong column type in xxx for column xxx. Found: float, expected: double precision
at org.hibernate.mapping.Table.validateColumns(Table.java:284)
at org.hibernate.cfg.Configuration.validateSchema(Configuration.java:1129)
at org.hibernate.tool.hbm2ddl.SchemaValidator.validate(SchemaValidator.java:139)
at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:360)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1340)
at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:867)
at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:670)

Strong Liu has suggested to change the default type mapping in org.hibernate.dialect.Oracle8iDialect
from
registerColumnType( Types.DOUBLE, "double precision" );
to
registerColumnType( Types.DOUBLE, "float" );

I have tried to create my own dialect to override the default behavior.

For example:

import org.hibernate.dialect.Oracle10gDialect;
import java.sql.Types;
public class Oracle11gDialectExt extends Oracle10gDialect {

public Oracle11gDialectExt()

}

And then set my own dialect in the persistence.xml, for example:
<property name="hibernate.dialect" value="jpa.test.hibernate.dialect.Oracle11gDialectExt" />

Then I don't see the error any more.