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https://issues.apache.org/jira/browse/CALCITE-4979?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17473152#comment-17473152
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Julian Hyde commented on CALCITE-4979:
--------------------------------------
If you are able to change your syntax, that's great. It will make it easier to
make the parser extensible. Note that in your dialect PREDICT would need to be
a reserved word.
Can you cleanup the markup in your description? Jira doesn't use backticks; it
uses double braces around single line code, and it uses a "code" tag before and
after multiline code blocks.
> Add support for extending parser to support additional select statements
> ------------------------------------------------------------------------
>
> Key: CALCITE-4979
> URL: https://issues.apache.org/jira/browse/CALCITE-4979
> Project: Calcite
> Issue Type: New Feature
> Components: extensions
> Affects Versions: 1.29.0
> Environment: * mac-arm64
> Reporter: Julian Bright
> Priority: Minor
>
> Calcite currently supports [extending the
> parser]([https://calcite.apache.org/docs/adapter.html#extending-the-parser)]
> with `config.fmpp` that has sections statements including alter and drop.
> I require the ability to introduce a custom `SELECT` like statement which
> requires adding adding an additional clause to the LeafQuery syntax in the
> `Parser.jj` file eg:
> {{ /**}}
> {{ * Parses a leaf in a query expression (SELECT, VALUES or TABLE).}}
> {{ */}}
> {{ SqlNode LeafQuery(ExprContext exprContext) :}}
> {{ {}}
> {{ SqlNode e;}}
> {{ }}}
> {{ {}}
> {{ {}}
> {{ // ensure a query is legal in this context}}
> {{ checkQueryExpression(exprContext);}}
> {{ }}}
> {{ e = SqlSelect() \{ return e; }}}
> {{ |}}
> {{ <#-- Add methods to parse additional select statements here -->}}
> {{ <#list
> (parser.selectStatementParserMethods!default.parser.selectStatementParserMethods)
> as method>}}
> {{ e = ${method} \{ return e; }}}
> {{ |}}
> {{ </#list>}}
> {{ e = TableConstructor() \{ return e; }}}
> {{ |}}
> {{ e = ExplicitTable(getPos()) \{ return e; }}}
> {{ }}}
> I would like to add a new section `selectStatementParserMethods` to the
> config eg:
> {{ # List of methods for parsing custom select statements.}}
> {{ selectStatementParserMethods: [}}
> {{ "SqlCustomSelect()"}}
> {{ ]}}
> Files required to be updated main codegen are:
> * core/src/main/codegen/templates/Parser.jj
> * core/src/main/codegen/default_config.fmpp
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