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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5901) You can declare user-defined functions which shadow builtin functions by the same name.
Date Mon, 13 Aug 2012 20:14:38 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13433486#comment-13433486

Rick Hillegas commented on DERBY-5901:

Here are some suggestions for how to address this issue:

1) We could make it illegal to declare a function whose unqualifed name would conflict with
the name of a builtin Derby function or operator. Existing functions which violate this rule
could be marked as invalid.

2) We could make all of these user-defined functions behave like the ABS case: Without a schema
qualifier, the name would resolve to the builtin function or operator. To specify the user-defined
function, you would have to qualify it with its schema name.

Here is my analysis of how these solutions would affect existing applications:


+ Existing code which invokes the user-defined functions would flat-out break, forcing the
application writer to fix the problem.
- Fixing the problem would be a two part process: i) drop the offending function and recreate
it with a non-conflicting name, then
ii) update existing invocations of the function across the application.


- Existing code which invokes the user-defined function might silently start using the builtin
function/operator rather than the user-defined function. This could produce wrong results.
+ Fixing the problem would just be a matter of adding a schema qualification to existing invocations.

Preferences? Other ideas? 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:
>            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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