[ 
https://issues.apache.org/jira/browse/CALCITE-4979?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
 ]

Julian Bright updated CALCITE-4979:
-----------------------------------
    Description: 
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

  was:
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


> 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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