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https://issues.apache.org/jira/browse/DERBY-4631?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13191655#comment-13191655
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Mamta A. Satoor commented on DERBY-4631:
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I stepped through the ConditionalNode's code generation logic to see how
"if..then..else.." code is generated. Based on that, I have following pseudo
code for code generation for solution 1). The following psuedo code is for
generating if(lefTablJoinColumnValue is null) then return
rightTableJoinColumnValue else return lefTablJoinColumnValue. I have not done
recent work in the code generation part and would appreciate feedback if the
psuedo code looks incorrect. I will next work on trying to identify how to make
this pseudo code kick in for ResultColumn code generation if we are dealing
with join column.
String receiverType = ClassName.DataValueDescriptor;
String resultTypeName =
getTypeCompiler(DataTypeDescriptor.getBuiltInDataTypeDescriptor(Types.BOOLEAN).getTypeId()).interfaceName();
//Following will generate if(lefTablJoinColumnValue is null)
//Then call generateExpression on left Table's column
LeftTableColumn.generateExpression(acb, mb);
mb.cast(receiverType); // cast the method instance
mb.callMethod(VMOpcode.INVOKEINTERFACE, (String) null,
"isNullOp",resultTypeName, 0);
mb.cast(ClassName.BooleanDataValue);
mb.push(true);
mb.callMethod(VMOpcode.INVOKEINTERFACE, (String) null,
"equals", "boolean", 1);
//Following will generate then part of the if condition by
generating expression for rightTablJoinColumnValue
mb.conditionalIf();
((ValueNode) RightTableColumn.generateExpression(acb, mb);
//Following will generate else part of the if condition by
generating expression for lefTablJoinColumnValue
mb.startElseCode();
((ValueNode) LeftTableColumn.generateExpression(acb, mb);
mb.completeConditional();
> Wrong join column returned by right outer join with NATURAL or USING and
> territory-based collation
> --------------------------------------------------------------------------------------------------
>
> Key: DERBY-4631
> URL: https://issues.apache.org/jira/browse/DERBY-4631
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.6.1.0
> Reporter: Knut Anders Hatlen
> Assignee: Mamta A. Satoor
> Labels: derby_triage10_8
>
> SQL:2003 says that the join columns in a natural join or in a named
> columns join should be added to the select list by coalescing the
> column from the left table with the column from the right table.
> Section 7.7, <joined table>, syntax rules:
> > 1) Let TR1 be the first <table reference>, and let TR2 be the <table
> > reference> or <table factor> that is the second operand of the
> > <joined table>. Let RT1 and RT2 be the row types of TR1 and TR2,
> > respectively. Let TA and TB be the range variables of TR1 and TR2,
> > respectively. (...)
> and
> > 7) If NATURAL is specified or if a <join specification> immediately
> > containing a <named columns join> is specified, then:
> (...)
> > d) If there is at least one corresponding join column, then let SLCC
> > be a <select list> of <derived column>s of the form
> >
> > COALESCE ( TA.C, TB.C ) AS C
> >
> > for every column C that is a corresponding join column, taken in
> > order of their ordinal positions in RT1.
> For a right outer join, Derby doesn't use COALESCE(TA.C, TB.C), but
> rather just TB.C (the column in the right table) directly.
> This is in most cases OK, because COALESCE(TA.C, TB.C) = TB.C is an
> invariant in a right outer join. (Because TA.C is either NULL or equal
> to TB.C.)
> However, in a database with territory-based collation, equality
> between two values does not mean they are identical, especially now
> that the strength of the collator can be specified (DERBY-1748).
> Take for instance this join:
> ij> connect
> 'jdbc:derby:testdb;create=true;territory=en_US;collation=TERRITORY_BASED:SECONDARY';
> ij> create table big(x varchar(5));
> 0 rows inserted/updated/deleted
> ij> insert into big values 'A','B','C';
> 3 rows inserted/updated/deleted
> ij> create table small(x varchar(5));
> 0 rows inserted/updated/deleted
> ij> insert into small values 'b','c','d';
> 3 rows inserted/updated/deleted
> ij> select x, t1.x, t2.x, coalesce(t1.x, t2.x) from small t1 natural right
> outer join big t2;
> X |X |X |4
> -----------------------
> A |NULL |A |A
> B |b |B |b
> C |c |C |c
> 3 rows selected
> I believe that the expected result from the above query is that the
> first column should have the same values as the last column. That is,
> the first column should contain {'A', 'b', 'c'}, not {'A', 'B', 'C'}.
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