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Date: Mon, 10 Jan 2005 23:48:17 -0800
From: Daniel John Debrunner <djd@debrunners.com>
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To: Derby Development <derby-dev@db.apache.org>
Subject: Re: (DERBY-13) Quoted names with embedded period mishandled in from
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Shreyas Kaushik wrote:

> Yes it does.
>
> Daniel John Debrunner wrote:
>
>>
>>Does the fix correctly implement duplicate name checking as detailed in
>>this mail?
>>
>>http://mail-archives.apache.org/eyebrowse/ReadMsg?listName=derby-dev@db.apache.org&msgNo=1569

Hmmm, I don't see how the change in FromList (extracted below) will
correctly handle

select ... FROM A.T1 as C, B.T2 as C

It seems that the leftTable variable will be set to <A.C> and rightTable
set to <B.C> which will not compare as equal. Am I missing something? If
the patch had tests I could see if this case was handled.

The code in FromList is not that clear to me, could be helped by
comments, and it concerns me that a TableName object is created out of a
schema name and a correlation name when such a construct has no valid
meaning. I see that you are hampered by the fact that there is no way to
tell if a correlation name has been used. In msgNo 1569 I laid out that
it would be best if there were two getExposed methods, but now I think a
single String getExposedName() will do, as long as it returns null if no
correlation name was used. That might have a ripple effect though the
code, but the best way to fix a bug is sometimes a minor rework, rather
than just band-aids on existing bad code. I think the fact that exposed
name handling has three bugs shows a re-work is needed. In any re-work I
would start out with explicitly stating how exposed names are handled
for a table in the from list and for a column reference, and then how
the two uses relate and compare.


Other comments on the patch are:

- - for the code extract below as a minor nit I would avoid using terms
like 'leftTable' or 'rightTable' unless left and right actual have
meaning, which they don't here. One table in a list is being compared
against the others in the list.

- - The other set of changes related to getAllResultColumns() again have
the possible issue of creating a TableName out of a schema name and
correlation name. I assume these are to fix derby-12, again comments
would be useful.

Also any comments you have on if this fixes Derby-18 and Derby-12 would
be helpful.

Dan.

- -				if (fromTable.getExposedName().equals
- -					(((FromTable) elementAt(index)).getExposedName()) )
+                leftTable = makeTableName(
fromTable.getTableName().getSchemaName(),
+
fromTable.getExposedName());
+
+                if(((FromTable) elementAt(index)).getTableName() == null) {
+                     rightTable =  makeTableName(null, ((FromTable)
elementAt(index)).getExposedName());
+                }
+
+                else {
+                    rightTable = makeTableName(((FromTable)
elementAt(index)).getTableName().getSchemaName(),
+                                                ((FromTable)
elementAt(index)).getExposedName());
+                }
+                if(leftTable.equals(rightTable))
 				{
 					throw
StandardException.newException(SQLState.LANG_FROM_LIST_DUPLICATE_TABLE_NAME,
fromTable.getExposedName());
 				}

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