fix: Add null check to UtilizedColumnAnalyzer

[auden-woolfson]

Description

Previously when using create table if not exists, the error if the table exists would look like this...

presto> create table if not exists tpch.sf1.customer as select * from tpch.sf1.customer;
CREATE TABLE: 0 rows

WARNING: Error in analyzing utilized columns for access control, falling back to checking access on all columns: Cannot invoke "java.util.List.iterator()" because "selectItems" is null


Query 20260206_233041_00001_z5bwk, FINISHED, 1 node
Splits: 1 total, 1 done (100.00%)
[Latency: client-side: 64ms, server-side: 35ms] [0 rows, 0B] [0 rows/s, 0B/s]

After these changes, we have a more descriptive and concise message...

presto> create table if not exists tpch.sf1.customer as select * from tpch.sf1.customer;
CREATE TABLE: 0 rows

WARNING: Table 'tpch.sf1.customer' already exists, skipping table creation


Query 20260206_233246_00000_bjt5x, FINISHED, 1 node
Splits: 1 total, 1 done (100.00%)
[Latency: client-side: 377ms, server-side: 209ms] [0 rows, 0B] [0 rows/s, 0B/s]

Motivation and Context

Impact

Test Plan

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Release Notes

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== RELEASE NOTES ==
General Changes
* Add warning message on CTAS if not exists

Summary by Sourcery

Bug Fixes:

• Prevent a potential null pointer error in UtilizedColumnsAnalyzer when analysis returns no output expressions for a query specification.

Summary by Sourcery

Guard query specification column utilization analysis when CREATE TABLE AS SELECT with IF NOT EXISTS resolves to a no-op due to an existing table, and surface a semantic warning in that scenario.

Bug Fixes:

• Prevent a potential null pointer when analyzing utilized columns for query specifications that have no output expressions, such as no-op CREATE TABLE IF NOT EXISTS statements.

Enhancements:

• Emit a semantic warning when CREATE TABLE IF NOT EXISTS is a no-op because the target table already exists, indicating that table creation is skipped.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adds a null check around output expressions in UtilizedColumnsAnalyzer to avoid NPEs for no-op CREATE TABLE AS SELECT, and emits a semantic warning when CREATE TABLE IF NOT EXISTS is a no-op because the target table already exists.

Sequence diagram for CREATE TABLE IF NOT EXISTS no-op handling

sequenceDiagram
    actor Client
    participant StatementAnalyzer
    participant MetadataResolver
    participant WarningCollector

    Client->>StatementAnalyzer: analyze CreateTableAsSelect
    activate StatementAnalyzer
    StatementAnalyzer->>MetadataResolver: tableExists(targetTable)
    MetadataResolver-->>StatementAnalyzer: boolean exists

    alt table exists AND node.isNotExists
        StatementAnalyzer->>StatementAnalyzer: analysis.setCreateTableAsSelectNoOp(true)
        StatementAnalyzer->>WarningCollector: add(PrestoWarning(SEMANIC_WARNING, "Table '%s' already exists, skipping table creation"))
        StatementAnalyzer-->>Client: Scope for rows BIGINT
    else table exists AND NOT node.isNotExists
        StatementAnalyzer-->>Client: throw SemanticException(TABLE_ALREADY_EXISTS)
    else table does not exist
        StatementAnalyzer->>StatementAnalyzer: proceed with table creation and query analysis
        StatementAnalyzer-->>Client: analysis result
    end
    deactivate StatementAnalyzer

Loading

Class diagram for UtilizedColumnsAnalyzer and StatementAnalyzer changes

classDiagram
    class UtilizedColumnsAnalyzer {
        - Analysis analysis
        + visitQuerySpecification(QuerySpecification querySpec, Context context) Void
    }

    class UtilizedColumnsAnalyzer_Context {
        + boolean prunable
        + List~FieldId~ getFieldIdsToExploreInRelation(QuerySpecification querySpec)
    }

    class FieldId {
        + int getFieldIndex()
    }

    class Analysis {
        + List~Expression~ getOutputExpressions(QuerySpecification querySpec)
        + void setCreateTableAsSelectNoOp(boolean value)
    }

    class QuerySpecification
    class Expression

    UtilizedColumnsAnalyzer --> Analysis : uses
    UtilizedColumnsAnalyzer --> UtilizedColumnsAnalyzer_Context : uses
    UtilizedColumnsAnalyzer_Context --> FieldId : returns
    UtilizedColumnsAnalyzer --> QuerySpecification : analyzes
    UtilizedColumnsAnalyzer --> Expression : processes

    %% StatementAnalyzer side
    class StatementAnalyzer {
        - MetadataResolver metadataResolver
        - WarningCollector warningCollector
        + visitCreateTableAsSelect(CreateTableAsSelect node, Optional_Scope scope) Scope
    }

    class MetadataResolver {
        + boolean tableExists(QualifiedObjectName table)
    }

    class WarningCollector {
        + void add(PrestoWarning warning)
    }

    class PrestoWarning {
        + PrestoWarning(StandardWarningCode code, String message)
    }

    class StandardWarningCode {
        <<enum>>
        SEMANTIC_WARNING
    }

    class CreateTableAsSelect {
        + boolean isNotExists()
    }

    class QualifiedObjectName
    class Scope
    class Optional_Scope

    StatementAnalyzer --> MetadataResolver : uses
    StatementAnalyzer --> WarningCollector : uses
    StatementAnalyzer --> CreateTableAsSelect : analyzes
    StatementAnalyzer --> Scope : returns
    StatementAnalyzer --> Optional_Scope : accepts
    WarningCollector --> PrestoWarning : collects
    PrestoWarning --> StandardWarningCode : uses
    MetadataResolver --> QualifiedObjectName : uses
    Analysis <.. StatementAnalyzer : shared in analysis flow

Loading

File-Level Changes

Change	Details	Files
Guard utilization analysis against missing output expressions from Analysis for certain query specifications.	Wrap usage of analysis.getOutputExpressions(querySpec) in a null check. Skip processing of select output expressions entirely when output expressions are null (e.g., for no-op statements). Keep existing behavior for both prunable and non-prunable contexts when output expressions are present.	presto-main-base/src/main/java/com/facebook/presto/sql/analyzer/UtilizedColumnsAnalyzer.java
Mark CREATE TABLE IF NOT EXISTS as a no-op with an explicit semantic warning when the target table already exists.	After detecting that the target table exists and NOT EXISTS is specified, set createTableAsSelectNoOp in Analysis. Add a PrestoWarning with StandardWarningCode.SEMANTIC_WARNING to inform the user that table creation is skipped because the table already exists. Return a scope with a single BIGINT 'rows' field for the no-op CTAS path, preserving prior behavior.	presto-main-base/src/main/java/com/facebook/presto/sql/analyzer/StatementAnalyzer.java

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[sourcery-ai]

Hey - I've left some high level feedback:

• In UtilizedColumnsAnalyzer.visitQuerySpecification, instead of silently skipping processing when selectItems is null, consider an early return with an assertion or check that documents this only happens for CTAS NOOP queries, so unexpected nulls in other code paths are easier to detect.
• For the new PrestoWarning in StatementAnalyzer.visitCreateTableAsSelect, consider using or introducing a more specific warning code than SEMANTIC_WARNING (and/or reusing the existing TABLE_ALREADY_EXISTS semantics) so downstream consumers can distinguish this case from other generic semantic warnings.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In `UtilizedColumnsAnalyzer.visitQuerySpecification`, instead of silently skipping processing when `selectItems` is null, consider an early return with an assertion or check that documents this only happens for CTAS NOOP queries, so unexpected nulls in other code paths are easier to detect.
- For the new `PrestoWarning` in `StatementAnalyzer.visitCreateTableAsSelect`, consider using or introducing a more specific warning code than `SEMANTIC_WARNING` (and/or reusing the existing TABLE_ALREADY_EXISTS semantics) so downstream consumers can distinguish this case from other generic semantic warnings.

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[aditi-pandit]

@auden-woolfson : Thanks for this code. Can you give an example of a query that you fixed with this change ?

[auden-woolfson]

@auden-woolfson : Thanks for this code. Can you give an example of a query that you fixed with this change ?

Sure...

Here is the behavior on the master branch

presto> create table if not exists tpch.sf1.customer as select * from tpch.sf1.customer;
CREATE TABLE: 0 rows

WARNING: Error in analyzing utilized columns for access control, falling back to checking access on all columns: Cannot invoke "java.util.List.iterator()" because "selectItems" is null


Query 20260206_233041_00001_z5bwk, FINISHED, 1 node
Splits: 1 total, 1 done (100.00%)
[Latency: client-side: 64ms, server-side: 35ms] [0 rows, 0B] [0 rows/s, 0B/s]

And with the changes...

presto> create table if not exists tpch.sf1.customer as select * from tpch.sf1.customer;
CREATE TABLE: 0 rows

WARNING: Table 'tpch.sf1.customer' already exists, skipping table creation


Query 20260206_233246_00000_bjt5x, FINISHED, 1 node
Splits: 1 total, 1 done (100.00%)
[Latency: client-side: 377ms, server-side: 209ms] [0 rows, 0B] [0 rows/s, 0B/s]

[pratyakshsharma]

Let us add a test case to cover this scenario?

Tests