[IOTDB-17798] Implement table model NEXT fill

[DaZuiZui]

Description

Add table-model NEXT fill syntax and planning

This PR implements FILL METHOD NEXT for the table model.

NEXT fills a null value with the nearest non-null value that appears later in the current operator input order. It directly copies the future value, does not interpolate, and does not search by timestamp order. If no next value exists, the value remains null.

The implementation supports:

• plain FILL METHOD NEXT
• TIME_BOUND
• TIME_COLUMN
• FILL_GROUP
• numeric, boolean, binary/text/string/blob/object, date, and timestamp columns

Plain NEXT does not require a helper/time column. A helper/time column is only required or inferred when TIME_BOUND or FILL_GROUP needs it.

FillPolicy.NEXT is appended after existing enum values to keep existing byte/ordinal compatibility, and TABLE_NEXT_FILL_NODE uses a new plan node type id.

Add NEXT fill plan node and optimizer support

This PR adds NextFillNode and wires it through serde, plan visitors, plan graph printing, pruning, symbol rewrite, analyzer, and planner logic.

For TIME_BOUND or FILL_GROUP, the analyzer resolves the required helper/time column similarly to PREVIOUS. For grouped fill, the planner reuses the existing fill-group sorting and grouping-symbol path.

PushLimitOffsetIntoTableScan treats NEXT like LINEAR and avoids pushing down LIMIT/OFFSET, because NEXT fill may need future rows that would otherwise be removed before filling.

Add NEXT fill execution path

This PR adds table NEXT fill operators and the generated fill implementation.

The execution layer reuses AbstractLinearFillOperator for cross-TsBlock look-ahead caching and grouped slicing. The NEXT fill algorithm scans the current value column from right to left, uses the nearest non-null candidate in the current block when available, and otherwise uses the first non-null candidate found in later cached blocks.

For grouped fill, group boundaries reset the next-value state so values are not filled across groups.

Tests

This PR adds and updates tests for:

• parsing FILL METHOD NEXT
• NextFillNode serde
• plain NEXT fill
• NEXT with TIME_BOUND
• NEXT with TIME_COLUMN
• NEXT with FILL_GROUP
• NEXT with TIME_BOUND + TIME_COLUMN + FILL_GROUP
• cross-TsBlock fill behavior
• group boundary isolation
• trailing null values
• helper/time column null handling
• boolean and binary/text-like values
• current input order semantics, including descending order and sorted subqueries
• LIMIT behavior without losing future next values

Closes #17798

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This PR has:

• been self-reviewed.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage.
• added integration tests.
• been tested in a test IoTDB cluster.

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Key changed/added classes (or packages if there are too many classes) in this PR

• RelationalSql.g4
• FillPolicy
• Fill
• AstBuilder
• StatementAnalyzer
• Analysis.NextFillAnalysis
• QueryPlanner
• NextFillNode
• PlanNodeType
• CommonPlanNodeDeserializer
• ICoreQueryPlanVisitor
• PlanGraphPrinter
• PruneFillColumns
• PushLimitOffsetIntoTableScan
• UnaliasSymbolReferences
• CommonOperatorUtils
• TableOperatorGenerator
• TableNextFillOperator
• TableNextFillWithGroupOperator
• fill/next/NextFill
• nextFill.ftl
• FillStatementTest
• NextFillNodeSerdeTest
• NextFillTest
• IoTDBFillTableIT

[JackieTien97]

Thanks for the thorough work here — this is a clean, well-structured PR. It faithfully mirrors the existing PREVIOUS/LINEAR fill machinery end to end (grammar → AST/AstBuilder → StatementAnalyzer/Analysis → QueryPlanner → optimizer rules → NextFillNode + serde → operators + freemarker codegen), and the visitor coverage looks complete: the generic visitFill fallbacks (SortElimination keeps the sort for non-ValueFill, TableDistributedPlanGenerator/TableModelTypeProviderExtractor) all handle NextFillNode correctly through inheritance, and every rule that special-cases fill nodes (PruneFillColumns, PushLimitOffsetIntoTableScan, UnaliasSymbolReferences, PlanGraphPrinter, TableOperatorGenerator) was updated. The 1043 node-type id is free and the serde order matches the siblings. Test coverage (parser / serde / fill execution / IT) is solid.

I've left a few minor, non-blocking comments inline — mostly test-coverage hardening plus one defensive note. The only item I'd like confirmation on before merge is the grouped cross-TsBlock reset path in TableNextFillWithGroupOperator#resetFill (see inline comment): it's correct for the cross-group case that's already tested, but the symmetric same-group look-ahead case isn't covered yet and is the one most sensitive to that reset condition.

[DaZuiZui]

Thanks for the review. The issue has been fixed. @JackieTien97

[DaZuiZui]

@JackieTien97 This failure looks like a self-hosted runner environment issue: mvn was not found before the integration tests started. Could you please rerun the failing check Table Cluster IT - 1C3D / Simple (17)?

[Copilot]

Pull request overview

This PR adds support for the table-model FILL METHOD NEXT syntax and execution, enabling “backward/next-value” fill semantics (fill nulls using the nearest later non-null value in the operator input order), including optional TIME_BOUND, TIME_COLUMN, and FILL_GROUP handling. It threads the feature end-to-end through grammar → AST → analyzer/planner → plan nodes/serde/visitors/optimizers → execution operators and codegen, and adds unit + integration tests.

Changes:

• Extend relational SQL grammar + AST/building/formatting to parse and print FILL METHOD NEXT with optional modifiers.
• Add NextFillNode and wire it through plan node types, serde, visitors, plan graph printing, and key optimizations (limit pushdown + pruning + unaliasing).
• Implement NEXT-fill execution via new table operators and a generated per-type NextFill implementation, with tests covering grouped fill, time-bound behavior, and cross-TsBlock look-ahead.

Reviewed changes

Copilot reviewed 27 out of 27 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
iotdb-core/relational-grammar/src/main/antlr4/org/apache/iotdb/db/relational/grammar/sql/RelationalSql.g4	Add NEXT alternative to the fillMethod grammar rule.
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/queryengine/plan/statement/component/FillPolicy.java	Add FillPolicy.NEXT with byte id 3.
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/queryengine/plan/relational/sql/util/CommonQuerySqlFormatter.java	Format NEXT fill similarly to PREVIOUS (TIME_BOUND/TIME_COLUMN/FILL_GROUP).
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/queryengine/plan/relational/sql/ast/Fill.java	Extend Fill AST to represent NEXT and add a constructor supporting PREVIOUS/NEXT.
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/queryengine/plan/relational/planner/node/PreviousFillNode.java	Fix equality/hash to include groupingKeys.
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/queryengine/plan/relational/planner/node/NextFillNode.java	Introduce NextFillNode plan node with serde and visitor support.
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/queryengine/plan/planner/plan/node/PlanNodeType.java	Register TABLE_NEXT_FILL_NODE type id 1043.
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/queryengine/plan/planner/plan/node/ICoreQueryPlanVisitor.java	Add visitNextFill default method.
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/queryengine/plan/planner/plan/node/CommonPlanNodeDeserializer.java	Deserialize NextFillNode for node type 1043.
iotdb-core/datanode/src/test/java/org/apache/iotdb/db/queryengine/plan/relational/sql/parser/FillStatementTest.java	Parser unit test for FILL METHOD NEXT with modifiers.
iotdb-core/datanode/src/test/java/org/apache/iotdb/db/queryengine/plan/relational/planner/NextFillNodeSerdeTest.java	Serde tests for NextFillNode + regression for PreviousFillNode equality.
iotdb-core/datanode/src/test/java/org/apache/iotdb/db/queryengine/execution/operator/process/fill/NextFillTest.java	Execution-level tests for NEXT fill, TIME_BOUND, object/binary behavior, and grouped fill.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/sql/parser/AstBuilder.java	Build Fill AST for NEXT fill.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/QueryPlanner.java	Plan FillPolicy.NEXT into a NextFillNode (and grouped path).
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/optimizations/UnaliasSymbolReferences.java	Support symbol unaliasing for NextFillNode.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/optimizations/PushLimitOffsetIntoTableScan.java	Disable limit/offset pushdown across NEXT fill.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/iterative/rule/PruneFillColumns.java	Ensure helper/grouping symbols are retained for NEXT fill.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/StatementAnalyzer.java	Analyze FillPolicy.NEXT and resolve helper/time column and grouping keys as needed.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/Analysis.java	Add Analysis.NextFillAnalysis.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/node/PlanGraphPrinter.java	Render NextFillNode details in plan graphs.
iotdb-core/calc-commons/src/main/java/org/apache/iotdb/calc/plan/planner/TableOperatorGenerator.java	Generate physical operators for NextFillNode (grouped and non-grouped).
iotdb-core/calc-commons/src/main/java/org/apache/iotdb/calc/plan/planner/CommonOperatorUtils.java	Add getNextFill() and refactor fill-filter creation.
iotdb-core/calc-commons/src/main/java/org/apache/iotdb/calc/execution/operator/process/TableNextFillWithGroupOperator.java	New grouped NEXT fill operator built on linear-fill caching/slicing.
iotdb-core/calc-commons/src/main/java/org/apache/iotdb/calc/execution/operator/process/TableNextFillOperator.java	New non-grouped NEXT fill operator.
iotdb-core/calc-commons/src/main/java/org/apache/iotdb/calc/execution/operator/process/fill/next/NextFill.java	NEXT fill algorithm implementation (right-to-left scan + cross-TsBlock look-ahead).
iotdb-core/calc-commons/src/main/codegen/templates/nextFill.ftl	Freemarker template generating per-type *NextFill implementations.
integration-test/src/test/java/org/apache/iotdb/relational/it/query/recent/IoTDBFillTableIT.java	Integration tests for NEXT fill semantics, modifiers, grouping, and error cases.

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[DaZuiZui]

Thanks for the review!

I have addressed the latest Copilot comments in this PR:

1. Added an explicit requireNonNull(fillMethod, "fillMethod is null") check in the Fill constructor before comparing the fill policy.

2. Removed the redundant groupSplitter state from TableNextFillWithGroupOperator, including its field, initialization, and add/remove bookkeeping. The grouped NEXT fill reset logic still relies on noMoreTsBlockForCurrentGroup, so the existing behavior is preserved.

I also verified the related test with:

mvn test -pl iotdb-core/datanode -am -Dtest=NextFillTest -DfailIfNoTests=false -Dsurefire.failIfNoSpecifiedTests=false -DskipITs

Result: Tests run: 5, Failures: 0, Errors: 0, Skipped: 0, BUILD SUCCESS.