Em 24/02/2013 23:44, Adrian Klaver escreveu:
On 02/24/2013 06:13 PM, Tom Duffey wrote:
Hi Everyone,
Riddle me this. I have a database column of type "real" that gets
mapped to a Java field of type double via JDBC. We have two
databases, test and production, and the test database is periodically
blown away and reloaded from a copy of production. We recently
noticed that some values do not match when viewed within our
application on test vs. production. More specifically:
- Selecting values from both test and production DBs using psql shows
"10.3885" as the value
- The Java app on production shows "10.3884573" while the test app
shows "10.3885"
I have a hunch that when the value was originally inserted into the
production DB it probably contained more than the 6 digits supported
by the real data type. It may have even been exactly the "10.3884573"
value we see when retrieving via JDBC on production. What I don't
understand is why when the value gets mapped back to Java via JDBC
those extra digits are coming back. Can anyone explain this or do you
think I'm on the wrong track? I stepped through code and it sure
seems like the extra information is coming back from the JDBC driver.
Are the production and test apps running on the same platform i.e. OS,
bitness, etc.
According to the Java Language specification, double and real are not
precise data types because the how it is stored in binary, which in turn
result in such errors.
See here:
http://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html
See also a discussion about how to overcome here:
http://stackoverflow.com/questions/179427/how-to-resolve-a-java-rounding-double-issue
This issue is not exclusive from Java, other languages based on IEEE 754
standard's suffer of same problem.
That's the reason because BigDecimal exists.
Regards,
Edson
Tom
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Tom Duffey
tduffey@xxxxxxxxxxxxxx
414-751-0600 x102
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