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https://issues.apache.org/jira/browse/TAJO-1565?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14502199#comment-14502199
]
ASF GitHub Bot commented on TAJO-1565:
--------------------------------------
Github user jihoonson commented on the pull request:
https://github.com/apache/tajo/pull/543#issuecomment-94330635
Ok. I found following quotes from the link you shard.
```
... A sort_expression can also be the column label or number of an output
column, ...
```
```
... There is still ambiguity if an ORDER BY item is a simple name that
could match either an output column name or a column from the table expression.
The output column is used in such cases. This would only cause confusion if you
use AS to rename an output column to match some other table column's name.
ORDER BY can be applied to the result of a UNION, INTERSECT, or EXCEPT
combination, but in this case it is only permitted to sort by output column
names or numbers, not by expressions.
```
The second quote looks to give a description related to this issue.
According to this quote, column labels, expressions, and numbers of each output
column can be resolved with the columns in the query's select list.
> 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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