Paul Rogers created IMPALA-7914:
-----------------------------------
Summary: Introduce AST base class/interface for statement-like
nodes
Key: IMPALA-7914
URL: https://issues.apache.org/jira/browse/IMPALA-7914
Project: IMPALA
Issue Type: Improvement
Components: Frontend
Affects Versions: Impala 3.0
Reporter: Paul Rogers
Assignee: Paul Rogers
The front-end is based on an abstract syntax tree (AST). The parser creates the
AST, the analyzer decorates it with semantic information, and the planner
creates a plan for it.
At present, the class hierarchy looks like this:
{noformat}
ParseNode
|-- Expr
| |-- <all expression nodes>
|-- FromClause
|-- <other statment fragments>
|-- StatementBase
| |-- SelectStmt
| |-- <other statements>
{noformat}
This is a nuisance because the only common base class for all statement-like
nodes is the {{ParseNode}}, which is also the common base class or expressions.
However, expressions and statement-like nodes behave differently during
analysis, SQL generation, and so on.
We propose to refactor the tree to introduce a new {{StmtNode}} interface or
class that defines the statement-like semantics, leaving {{Expr} to define the
expression-like semantics. The methods then move out of {{ParseNode}}.
This change all allow revising the analysis step as follows:
* Analysis of statement-like nodes is done "in place"
* Analysis of expression nodes may result in replacing one node with a
rewritten version
Similarly, when generating SQL:
* Statements provide the option of generating before- or after-rewrite SQL.
* Expressions can only generate SQL for what they are; they have no concept of
before- or after- rewrites.
Specifically:
{noformat}
ParseNode
|-- Expr
| |-- <all expression nodes>
|-- StmtNode
| |-- FromClause
| |-- <other statment fragments>
| |-- StatementBase
| | |-- SelectStmt
| | |-- <other statements>
{noformat}
It may be useful to introduce a {{ClauseNode}}, but we'll see if that is
actually helpful as we do the refactoring:
{noformat}
|-- StmtNode
| |-- ClauseNode
| | |-- FromClause
| | |-- <other statment fragments>
| |-- StatementBase
| | |-- SelectStmt
| | |-- <other statements>
{noformat}
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