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https://issues.apache.org/jira/browse/TAJO-1565?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14501855#comment-14501855
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ASF GitHub Bot commented on TAJO-1565:
--------------------------------------
Github user jihoonson commented on the pull request:
https://github.com/apache/tajo/pull/543#issuecomment-94278974
Sorry for confusing you. I mean, this issue is related to SQL name
resolution rules rather than sort execution.
Basically, when there are two or more columns that have the same name in a
SQL, qualifiers must be explicitly specified for those columns. Tajo also
follows this rule so far. And now, you are trying to add a new rule.
The general rule means that the new rule should be sufficiently general to
handle most cases with a few unavoidable exceptions. So, we need to discuss to
design the new rule. Without discussion, people like me can have many questions
about the rule. For example, your patch allows to omit the qualifier of a
column in the order-by clause if the select clause involves a column of the
same name. So, some of my questions are, why this rule focuses on only order-by
clause? why does the same rule can be applied to group-by clauses or any other
clauses? what happens if the select and order-by clauses involve two or more
columns?
I've also checked pgsql. It seems to use this rule for only the order-by
clause. I think that we need the exact reason to make a solid rule.
The above quote looks to describe the order-by clause, and not much helpful
to investigate this issue.
> Simple column name in ORDER BY is failed with "Ambiguous Column Name ERROR".
> ----------------------------------------------------------------------------
>
> Key: TAJO-1565
> URL: https://issues.apache.org/jira/browse/TAJO-1565
> Project: Tajo
> Issue Type: Bug
> Affects Versions: 0.10.0
> Reporter: Hyoungjun Kim
> Assignee: Dongjoon Hyun
> Attachments: TAJO-1565.Hyun.150419.0.patch.txt
>
>
> I ran the following query which contains self join and doesn't use a fully
> qualified column name in ORDER BY clause. The query failed with "Ambiguous
> Column Name ERROR".
> {code:sql}
> select n1.n_nationkey, n2.n_name
> from nation n1, nation n2, nation n3
> where n1.n_nationkey = n2.n_nationkey
> and n1.n_nationkey = n3.n_nationkey
> order by n_name;
> {code}
> {noformat}
> org.apache.tajo.plan.algebra.AmbiguousFieldException: ERROR: column name
> Ambiguous Column Name: default.n1.n_name (TEXT), default.n2.n_name (TEXT),
> default.n3.n_name (TEXT) is ambiguous
> at
> org.apache.tajo.plan.nameresolver.NameResolver.ensureUniqueColumn(NameResolver.java:286)
> at
> org.apache.tajo.plan.nameresolver.NameResolver.resolveFromAllRelsInBlock(NameResolver.java:183)
> at
> org.apache.tajo.plan.nameresolver.ResolverByLegacy.resolveColumnWithoutQualifier(ResolverByLegacy.java:104)
> at
> org.apache.tajo.plan.nameresolver.ResolverByLegacy.resolve(ResolverByLegacy.java:44)
> at
> org.apache.tajo.plan.nameresolver.NameResolver.resolve(NameResolver.java:90)
> at
> org.apache.tajo.plan.ExprNormalizer.visitColumnReference(ExprNormalizer.java:344)
> at
> org.apache.tajo.plan.ExprNormalizer.visitColumnReference(ExprNormalizer.java:84)
> at
> org.apache.tajo.plan.algebra.BaseAlgebraVisitor.visit(BaseAlgebraVisitor.java:218)
> at
> org.apache.tajo.plan.visitor.SimpleAlgebraVisitor.visit(SimpleAlgebraVisitor.java:43)
> at
> org.apache.tajo.plan.ExprNormalizer.normalize(ExprNormalizer.java:122)
> at
> org.apache.tajo.plan.ExprNormalizer.normalize(ExprNormalizer.java:115)
> at
> org.apache.tajo.plan.LogicalPlanner.visitSort(LogicalPlanner.java:829)
> at org.apache.tajo.plan.LogicalPlanner.visitSort(LogicalPlanner.java:66)
> at
> org.apache.tajo.plan.algebra.BaseAlgebraVisitor.visit(BaseAlgebraVisitor.java:65)
> at
> org.apache.tajo.plan.LogicalPlanner.visitProjection(LogicalPlanner.java:238)
> at
> org.apache.tajo.plan.LogicalPlanner.visitProjection(LogicalPlanner.java:66)
> at
> org.apache.tajo.plan.algebra.BaseAlgebraVisitor.visit(BaseAlgebraVisitor.java:59)
> at
> org.apache.tajo.plan.LogicalPlanner.createPlan(LogicalPlanner.java:143)
> at
> org.apache.tajo.plan.LogicalPlanner.createPlan(LogicalPlanner.java:131)
> at
> org.apache.tajo.master.GlobalEngine.createLogicalPlan(GlobalEngine.java:271)
> at
> org.apache.tajo.master.GlobalEngine.executeQuery(GlobalEngine.java:188)
> at
> org.apache.tajo.master.TajoMasterClientService$TajoMasterClientProtocolServiceHandler.submitQuery(TajoMasterClientService.java:287)
> at
> org.apache.tajo.ipc.TajoMasterClientProtocol$TajoMasterClientProtocolService$2.callBlockingMethod(TajoMasterClientProtocol.java:543)
> at
> org.apache.tajo.rpc.BlockingRpcServer$ServerHandler.channelRead(BlockingRpcServer.java:113)
> at
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:308)
> at
> io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:294)
> at
> io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:103)
> at
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:308)
> at
> io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:294)
> at
> io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:182)
> at
> io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:308)
> at
> io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:294)
> at
> io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:846)
> at
> io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:130)
> at
> io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:511)
> at
> io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:468)
> at
> io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:382)
> at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:354)
> at
> io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116)
> at java.lang.Thread.run(Thread.java:744)
> {noformat}
> This query run successfully on PostgreSQL.
> {noformat}
> babokim=# select n1.n_nationkey, n2.n_name
> babokim-# from nation n1, nation n2, nation n3
> babokim-# where n1.n_nationkey = n2.n_nationkey
> babokim-# and n1.n_nationkey = n3.n_nationkey
> babokim-# order by n_name;;
> n_nationkey | n_name
> -------------+-----------
> 0 | ALGERIA
> 1 | ARGENTINA
> 2 | BRAZIL
> (3 rows)
> {noformat}
> Also I found a strange code in NameResolver.ensureUniqueColumn().
> I think "else if (candidates.size() > 2)" statement should be "else". I don't
> know why compare great than 2.
> {code:java}
> static Column ensureUniqueColumn(List<Column> candidates) throws
> VerifyException {
> if (candidates.size() == 1) {
> return candidates.get(0);
> } else if (candidates.size() > 2) {
> StringBuilder sb = new StringBuilder();
> boolean first = true;
> for (Column column : candidates) {
> if (first) {
> first = false;
> } else {
> sb.append(", ");
> }
> sb.append(column);
> }
> throw new AmbiguousFieldException("Ambiguous Column Name: " +
> sb.toString());
> } else {
> return null;
> }
> }
> {code}
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