confluentinc/ksql

Variable substitution doesn't work with field names in projection or where clause

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#8,250 opened on Oct 12, 2021

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 (12 comments) (0 reactions) (1 assignee)Java (1,048 forks)batch import
bugfix-it-weekgood first issuestreaming-enginevariable-substitution

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Description

Describe the bug Variable substitution fails for field names in the query projection or where clause. According to example in docs here, it should work.

To Reproduce Version: 6.2.1

ksql> define colName1 = 'LEVEL';
ksql> select ${colName1} from ksql_processing_log emit changes;
Illegal argument at Line: 1, Col: 8. Got: 'LEVEL'
Statement: select ${colName1} from ksql_processing_log emit changes;

ksql> define colName1 = 'LEVEL';
ksql> select * from ksql_processing_log where ${colName1} = 'ERROR';
Illegal argument at Line: 1, Col: 41. Got: 'LEVEL'
Statement: select * from ksql_processing_log where ${colName1} = 'ERROR';

Expected behavior Query succeeds, substituting variable (colName1) value for field name.

Actual behaviour See above for error details.

Additional context Initial feedback from @spena:

Seems the parser is detecting the ${colName1} from the where clause as a variable literal and not a variable identifier, so the parsing fails because level is not a string literal

Contributor guide

Research direction
Investigate how variable substitution is implemented in the ksqlDB parser. Focus on the logic that handles variable identifiers vs string literals. The error suggests that the parser is treating the variable substitution as a literal instead of an identifier. Check the substitution context and the grammar rules for column references.
Tech stack
javasql
Domain
databasebackend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GitJava
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70