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https://issues.apache.org/jira/browse/DERBY-5901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13451678#comment-13451678
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Kathey Marsden commented on DERBY-5901:
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I think the most likely trouble for existing applications with option 1 would
be if someone implemented a function before it was added as a builtin function
in Derby later. For example these added in 10.3:
https://issues.apache.org/jira/browse/DERBY-1808
Similarly if an application written against 10.9 creates a function by the
same name as a builtin function that is added sometime in the future, it
would also break when upgraded to the new derby version which has the new
builtin function.
I am not sure what the correct answer is but wonder if the standard speaks to
this point wrt non-reserved words like SIN and what other database products do.
I am concerned about introducing an incompatibility that is not specific to
one release but has the potential to create an incompatibility for every
function added at a time when the likely affected applications are quite old
and possibly don't have developers ready to investigate and fix such an issue.
> 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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