[DISCUSS] Add FROM-First-syntax support to IoTDB Table Mode

[Abdelrahman Mostafa]

Hi all,

I would like to propose adding support for FROM-first syntax to IoTDB's
Table SQL dialect.

*This feature improves the user experience in the following ways:*

   - Better IDE/CLI auto-completion: The IDE knows the table schema before
   the SELECT clause, enabling intelligent column suggestions
   - Logical flow alignment: FROM-first syntax aligns better with the
   actual execution order, and the human thought process defines the source
   first, then filter, then project
   - Quick data exploration: Instead of writing SELECT * FROM sensors, you
   simply write FROM sensors

For more details, please refer to the GitHub issue:
https://github.com/apache/iotdb/issues/17336

*Proposed Syntax:*
Add a new grammar rule to RelationalSql.g4:

fromFirstQuerySpecification
    : FROM relation (',' relation)*
      (SELECT setQuantifier? selectItem (',' selectItem)*)?
      (WHERE where=booleanExpression)?
      (GROUP BY groupBy)?
      (HAVING having=booleanExpression)?
      (WINDOW windowDefinition (',' windowDefinition)*)?
    ;

Add the new rule as an alternative to queryPrimary:

queryPrimary
    : querySpecification                   #queryPrimaryDefault
    | TABLE qualifiedName                  #table
    | VALUES expression (',' expression)*  #inlineTable
    | '(' queryNoWith ')'                  #subquery
    | fromFirstQuerySpecification          #fromFirstQuery    // NEW
    ;

*Usage Examples:*

-- Current syntax

SELECT temperature, humidity FROM sensors WHERE time >= 10;

-- Proposed FROM-first syntax

 FROM sensors SELECT temperature, humidity WHERE time >= 10;

-- Quick exploration (omitting SELECT implies SELECT *)

FROM sensors LIMIT 10;

*Implementation Approach:*

   1. Grammar Update: Add fromFirstQuerySpecification rule to
   RelationalSql.g4
   2. AST Builder: Add visitFromFirstQuerySpecification() in
   AstBuilder.java, reusing the existing visitQuerySpecification() logic with
   added handling for the omitted SELECT clause implying SELECT *
   3. Testing: Add integration tests covering all new syntax scenarios
   4. Documentation: Update IoTDB docs with usage examples and sample use
   cases

*Note:* This is an additive feature for Table mode only; the traditional
SELECT ... FROM ... syntax will remain fully supported.

I will begin implementation once the community confirms the design.
My GitHub handle is @Abdelrahman-358 if you would like to assign the issue
to me.

Any feedback or comments are welcome.

Best regards,
Abdelrahman