GitHub user cloud-fan opened a pull request:
https://github.com/apache/spark/pull/2230
SPARK-2096 Correctly parse dot notations
First let me write down the current `projections` grammar of spark sql:
expression : orExpression
orExpression : andExpression {"or" andExpression}
andExpression : comparisonExpression {"and"
comparisonExpression}
comparisonExpression : termExpression | termExpression "="
termExpression | termExpression ">" termExpression | ...
termExpression : productExpression {"+"|"-"
productExpression}
productExpression : baseExpression {"*"|"/"|"%" baseExpression}
baseExpression : expression "[" expression "]" | "("
expression ")" | ident | ...
ident : identChar {identChar | digit} | delimiters
| ...
identChar : letter | "_" | "."
delimiters : "," | ";" | "(" | ")" | "[" | "]" | ...
projection : expression [["AS"] ident]
projections : projection { "," projection}
For something like `a.b.c[1]`, it will be parsed as:
<img src="http://img51.imgspice.com/i/03008/4iltjsnqgmtt_t.jpg"; border=0>
But for something like `a[1].b`, the current grammar can't parse it
correctly.
A simple solution is written in `ParquetQuerySuite#NestedSqlParser`,
changed grammars are:
identChar : letter | "_"
baseExpression : expression "[" expression "]" | expression
"." ident | "(" expression ")" | ident | ...
This works well, but can't cover some corner case like `select t.a.b from
table as t`:
<img src="http://img51.imgspice.com/i/03008/v2iau3hoxoxg_t.jpg"; border=0>
`t.a.b` parsed as `GetField(GetField(UnResolved("t"), "a"), "b")` instead
of `GetField(UnResolved("t.a"), "b")` using this new grammar.
However, we can't resolve `t` as it's not a filed, but the whole table.(if
we could do this, then `select t from table as t` is legal, which is unexpected)
My solution is:
dotExpressionHeader : ident "." ident
baseExpression : expression "[" expression "]" |
dotExpressionHeader | expression "." ident | "(" expression ")" | ident | ...
I passed all test cases under sql locally and add a more complex case.
I'm not familiar with the latter optimize phase, please correct me if I
missed something.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/cloud-fan/spark dot
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/2230.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 #2230
----
commit de630829028d9d4a7ef55b8a0ff31e09f0b549d9
Author: Wenchen Fan <[email protected]>
Date: 2014-09-01T11:10:02Z
SPARK-2096 Correctly parse dot notations
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