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https://issues.apache.org/jira/browse/DERBY-4631?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13188739#comment-13188739
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Mamta A. Satoor commented on DERBY-4631:
----------------------------------------
With solution 1), we will need to know where the current code generation
happens for join columns. Solution 1) requires that we change the code
generation to following logic.
1)if the left table's join column value is null then pick up the right table's
join column's value.
2)If the left table's join column value is non-null, then pick up that value
Following is what I found while looking for code generation logic for the join
columns.
In the bind phase of a query, we start looking at result columns and assigning
virutal column numbers to them (impl.sql.compile.ResultColumn:virtualColumnId).
These virtual column ids are used to find mapping for those columns into
runtime resultset for the query.
connect
'jdbc:derby:db1;create=true;territory=en_US;collation=TERRITORY_BASED:SECONDARY';
CREATE TABLE derby4631_t1(x varchar(5));
INSERT INTO derby4631_t1 VALUES 'A','B';
CREATE TABLE derby4631_t2(x varchar(5));
INSERT INTO derby4631_t2 VALUES 'b','c';
SELECT x FROM derby4631_t2 NATURAL RIGHT OUTER JOIN derby4631_t1;
For the NATURAL JOIN query above, an equi-join is generated which will be
derby4631_t2.x = derby4631_t1.x. For this equi join, the join column x from
left table(derby4631_t2) will get virtual column id of 1 and join column x from
right table(derby4631_t1) will get virtual column id of 2. The column x in the
SELECT query in Derby today gets associated with right table in case of RIGHT
OUTER JOIN and hence that column's virtual column id is also 2. At the time of
code generation, we use this information to decide what column position from
the run time resultset would be used to get the values. Following is the stack
trace of where the code generation for join column happens.
Thread [main] (Suspended (breakpoint at line 1421 in ProjectRestrictNode))
ProjectRestrictNode.generateMinion(ExpressionClassBuilder,
MethodBuilder, boolean) line: 1421
ProjectRestrictNode.generate(ActivationClassBuilder, MethodBuilder)
line: 1334
ScrollInsensitiveResultSetNode.generate(ActivationClassBuilder,
MethodBuilder) line: 109
CursorNode.generate(ActivationClassBuilder, MethodBuilder) line: 641
CursorNode(StatementNode).generate(ByteArray) line: 345
GenericStatement.prepMinion(LanguageConnectionContext, boolean,
Object[], SchemaDescriptor, boolean) line: 518
GenericStatement.prepare(LanguageConnectionContext, boolean) line: 97
GenericLanguageConnectionContext.prepareInternalStatement(SchemaDescriptor,
String, boolean, boolean) line: 1103
EmbedStatement40(EmbedStatement).execute(String, boolean, boolean, int,
int[], String[]) line: 610
EmbedStatement40(EmbedStatement).execute(String) line: 559
ij.executeImmediate(String) line: 367
utilMain.doCatch(String) line: 527
utilMain.runScriptGuts() line: 369
utilMain.go(LocalizedInput[], LocalizedOutput) line: 245
Main.go(LocalizedInput, LocalizedOutput) line: 229
Main.mainCore(String[], Main) line: 184
Main.main(String[]) line: 75
ij.main(String[]) line: 59
> 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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