[CALCITE-7316] The POSITION function in SQLite is missing the FROM clause

[macroguo-ghy]

Jira Link

CALCITE-7316

Changes Proposed

This PR fixes SQLite SQL generation for the 3-argument POSITION form so that the FROM start position is preserved instead of being dropped.

Reproduction:

select position(''C'' IN ''ABCABC'' FROM 4) from "product";

Before this change, the generated SQLite SQL lost the FROM 4 semantics.

This change rewrites the SQLite form to an equivalent expression based on SUBSTR and INSTR, and adds SQLite rel-to-sql tests covering both a hit and a miss case for POSITION(... FROM ...).

[caicancai]

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[Copilot]

Pull request overview

Fixes SQLite SQL generation for the 3-argument POSITION(... FROM ...) form so the start-position semantics are preserved during unparsing.

Changes:

• Update SqliteSqlDialect to unparse 3-arg POSITION into a CASE expression based on SUBSTR + INSTR.
• Add rel-to-sql tests for SQLite covering both a match and a no-match case for POSITION(... FROM ...).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
core/src/main/java/org/apache/calcite/sql/dialect/SqliteSqlDialect.java	Adds operand-count-sensitive POSITION unparsing and a helper to rewrite the 3-arg form for SQLite.
core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java	Adds SQLite rel-to-sql assertions for POSITION(... FROM ...) (hit + miss).

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[Copilot]

In the 3-arg POSITION rewrite, the CASE expression uses ELSE 0. If any operand is NULL, INSTR(...) (and therefore relativePosition) becomes NULL; the WHEN relativePosition > 0 condition then evaluates to NULL and the CASE falls through to ELSE 0, changing the result from NULL to 0. To preserve POSITION/INSTR null-propagation semantics, make the ELSE branch return relativePosition (so it yields 0 on “not found” and NULL on NULL inputs), or add an explicit WHEN relativePosition IS NULL THEN NULL branch.

Suggested change

	SqlNodeList.of(thenResult), SqlLiteral.createExactNumeric("0", pos));
	SqlNodeList.of(thenResult), SqlNode.clone(relativePosition));

[xiedeyantu]

Thank you for taking the time to address the Jira issue I raised. I’ve left a few points open for discussion—perhaps we can continue the conversation there in the Jira ticket as well.

[xiedeyantu]

Why do we need to add additional function definitions in the dialect?

[xiedeyantu]

I’m not sure if we need to make such complex rewrites. Honestly, I haven’t even figured out how to approach the rewrite in the Jira issue.

[xuzifu666]

+1. Additionally, there is another issue: for the query select * from db.table where d=position(a IN b FROM c), if this expression is placed within the WHERE clause, we still need to enclose it in parentheses.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
93.9% Coverage on New Code
0.0% Duplication on New Code

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