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https://issues.apache.org/jira/browse/DERBY-5901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13452168#comment-13452168
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Rick Hillegas commented on DERBY-5901:
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The Standard only addresses the situation where the operator/function name is a
reserved word. For instance, DATE is a reserved word under the Standard and so
an application should not be allowed to create a function called DATE--Derby
allows this and this creates a conflict with the builtin Derby DATE operator.
The Standard is silent on operator/function names which are not reserved words.
So, for instance, the Standard has nothing to say about whether an application
can create a function called ABS or SIN. Note that these are both the names of
JDBC escape functions. We would not have a problem with these operator names if
Derby only invoked them via JDBC escape syntax.
But like other RDBMSes, Derby can declare its own operators on top of those
defined by the Standard. As we go forward, we should be careful to not enlarge
the problem described by this JIRA. That is, if we add new operators, we should
make sure that they cannot collide with the names of application-defined
functions.
I don't see how to address this issue without introducing a backward
incompatibility. Regardless of the approach we take, we could add a scrap of
upgrade logic which looks for conflicting application-defined function names.
If we find a conflict, we could fail the upgrade with a message advising the
user that the conflict needs to be fixed first.
Thanks,
-Rick
> You can declare user-defined functions which shadow builtin functions by the
> same name.
> ---------------------------------------------------------------------------------------
>
> Key: DERBY-5901
> URL: https://issues.apache.org/jira/browse/DERBY-5901
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.10.0.0
> Reporter: Rick Hillegas
>
> You can override a Derby builtin function by creating a function with the
> same name. This can give rise to wrong results.
> Consider the following user code:
> public class FakeSin
> {
> public static Double sin( Double input ) { return new Double( 3.0 ); }
> }
> Now run the following script:
> connect 'jdbc:derby:memory:db;create=true';
> values sin( 0.5 );
> create function sin( a double ) returns double language java parameter style
> java no sql external name 'FakeSin.sin';
> values sin( 0.5 );
> values sin( 0.5 );
> Note the following:
> 1) The first invocation of sin() returns the expected result.
> 2) You are allowed to create a user-defined function named "sin" which can
> shadow the builtin function.
> 3) The second invocation of sin() returns the result of running the builtin
> function. This is because the second invocation is character-for-character
> identical to the first, so Derby just uses the previously prepared statement.
> 4) But the third invocation of sin() returns the result of running the
> user-defined function. Note that the third invocation has an extra space in
> it, which causes Derby to compile it from scratch, picking up the
> user-defined function instead of the builtin one.
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