GitHub user cloud-fan opened a pull request:
https://github.com/apache/spark/pull/11658
[SPARK-XXXX][SQL] Can't add subquery to an operator with same-name outputs
while generate SQL string
## What changes were proposed in this pull request?
This PR tries to solve a fundamental issue in the `SQLBuilder`. When we
want to turn a logical plan into SQL string and put it after FROM clause, we
need to wrap it with a sub-query. However, a logical plan is allowed to have
same-name outputs with different qualifiers(e.g. the `Join` operator), and this
kind of plan can't be put under a subquery as we will erase and assign a new
qualifier to all outputs and make it impossible to distinguish same-name
outputs.
To solve this problem, this PR renames all attributes with globally unique
names(using exprId), so that we don't need qualifiers to resolve ambiguity
anymore.
## How was this patch tested?
existing tests and new tests in LogicalPlanToSQLSuite.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/cloud-fan/spark gensql
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/11658.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #11658
----
commit f4b1ae8b30c2a572d4f44cd68b66c224aeee553b
Author: Wenchen Fan <wenc...@databricks.com>
Date: 2016-03-11T06:29:45Z
tmp
commit 198b406a643d908483408ec6ccea26ffdc464aa9
Author: Wenchen Fan <wenc...@databricks.com>
Date: 2016-03-11T14:35:50Z
assign globally unique names to all attributes to avoid ambiguity
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