[Feat] Add table less query for table model

[FearfulTomcat27]

This pull request adds support for SQL queries without a FROM clause (table-less queries) in the IoTDB query engine, along with corresponding tests and necessary planning and execution logic updates. The changes ensure that expressions such as SELECT 1+1, SELECT sin(1), or SELECT COUNT(*) can be parsed, planned, and executed correctly, producing the expected single-row results even when no table is specified.

Key changes include:

Support for Table-less (No-FROM) Queries:

• Updated the query planner (QueryPlanner.java) to generate a ValuesNode with a single row when a SELECT statement does not have a FROM clause, enabling implicit single-row semantics for such queries.
• Modified the execution plan generator (TableOperatorGenerator.java) to correctly produce a ValuesOperator with the appropriate number of rows and columns for no-FROM queries, using a RunLengthEncodedColumn to simulate the required rows.

Testing:

• Added a new test case (testTableLessQuery) in IoTDBComplexQueryIT.java to verify correct behavior for queries without a FROM clause, including arithmetic, function, formatting, and aggregation expressions.

Planner and Optimizer Enhancements:

• Implemented getOutputSymbols in ValuesNode to support symbol mapping and output column handling in the planner.
• Updated the unaliasing optimizer (UnaliasSymbolReferences.java) to handle ValuesNode, ensuring correct symbol mapping and row transformation in the optimization pipeline.

Dependency and Import Updates:

• Added necessary imports for new classes and types used in the planner and operator generator, such as ValuesNode, InternalTypeManager, and RunLengthEncodedColumn. [1] [2] [3] [4]

[Copilot]

Pull request overview

Adds support for table-model SQL queries without a FROM clause by introducing an implicit single-row source in the relational planner and enabling execution/optimization to handle it, plus an integration test.

Changes:

• Update relational planning to produce a ValuesNode (1 row) when FROM is absent.
• Extend optimizer (UnaliasSymbolReferences) and plan node (ValuesNode) to expose/migrate output symbols for ValuesNode.
• Update table execution planning to generate a ValuesOperator that can emit the implicit single row for no-FROM queries; add IT coverage.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/QueryPlanner.java	Plans no-FROM queries as a single-row ValuesNode source.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/optimizations/UnaliasSymbolReferences.java	Adds unalias rewriting support for ValuesNode.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/node/ValuesNode.java	Implements getOutputSymbols() so planner/optimizers can treat ValuesNode consistently.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/TableOperatorGenerator.java	Generates a non-empty ValuesOperator for the implicit single-row source case.
integration-test/src/test/java/org/apache/iotdb/relational/it/query/recent/IoTDBComplexQueryIT.java	Adds an integration test for table-less queries.

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[Copilot]

This assertion is likely flaky because it compares ResultSet.getString() output against Double.toString(Math.sin(1))/cos/tan. JDBC/IoTDB formatting (precision, trailing zeros, scientific notation, locale) can differ from Java's Double.toString, causing intermittent failures. Consider using tableResultSetEqualByDataTypeTest (double comparison with delta) or explicitly formatting/rounding in SQL (e.g., ROUND(sin(1), n)) so the returned strings are deterministic.

Suggested change

	retArray =
	new String[] {Math.sin(1) + "," + Math.cos(1) + "," + Math.tan(1) + ","};
	tableResultSetEqualTest(
	"SELECT sin(1), cos(1), tan(1)", expectedHeader, retArray, DATABASE_NAME);
	retArray = new String[] {"0.841471,0.540302,1.557408,"};
	tableResultSetEqualTest(
	"SELECT round(sin(1), 6), round(cos(1), 6), round(tan(1), 6)",
	expectedHeader,
	retArray,
	DATABASE_NAME);