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Date: Mon, 2 Dec 2013 13:38:37 +0000 (UTC)
From: "Rick Hillegas (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Message-ID: <JIRA.12603246.1344868395458.53825.1385991517623@arcas>
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Subject: [jira] [Commented] (DERBY-5901) You can declare user-defined
 functions which shadow builtin functions by the same name.
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    [ https://issues.apache.org/jira/browse/DERBY-5901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13836511#comment-13836511 ] 

Rick Hillegas commented on DERBY-5901:
--------------------------------------

Emptying the statement cache when a shadowing function is created sounds like a cheap, adequate fix for this rare edge-case. Thanks.

> 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: 10.10.1.1
>            Reporter: Rick Hillegas
>              Labels: derby_triage10_10
>
> 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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