DECIMAL(38,18) / DECIMAL(38,18) silently returns NULL due to overflow, while equivalent multiplication works correctly

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Beschreibung

Issue

When dividing two DECIMAL(38,18) values (the maximum supported decimal precision in StarRocks), the result silently returns NULL due to precision overflow. The equivalent operation using multiplication with POW(..., -1) returns the correct result.

Steps to reproduce Returns NULL (bug)

SELECT CAST(2672.925686105492400095 AS DECIMAL(38,18))
     / CAST(421.193403692563637349 AS DECIMAL(38,18));

Returns 6.346076796721411 (works)

SELECT CAST(2672.925686105492400095 AS DECIMAL(38,18))
     * POW(CAST(421.193403692563637349 AS DECIMAL(38,18)), -1);

Workaround: explicit CAST to DOUBLE before division (works)

SELECT CAST(CAST(2672.925686105492400095 AS DECIMAL(38,18)) AS DOUBLE)
     / CAST(CAST(421.193403692563637349 AS DECIMAL(38,18)) AS DOUBLE);

Expected behavior

The session variable decimal_overflow_to_double should apply to the / operator the same way it applies to *.

Actual behavior

Division of two DECIMAL(38,18) values silently returns NULL. No error, no warning.

Starrocks version: 3.5.14

Contributor Guide

Research-Richtung: Investigate the division operator implementation for DECIMAL(38,18) in StarRocks. Compare the overflow handling logic between division and multiplication. Check if the `decimal overflow to double` session variable is properly applied to division. Look at the source code in the repository, possibly in `src/exprs/` or `fe/fe core/src/main/java/com/starrocks/expression/`. Examine the behavior when the result precision exceeds 38 and see if casting to double is a viable workaround. Ensure that the fix aligns with the existing multiplication behavior.
Tech Stack: javasql
Domain: backenddatabase
Issue Type: Fehler
Schwierigkeit: 3
Geschätzte Zeit: Halber Tag
Aktivitätsstatus: Frisch
Klarheit: Klar
Voraussetzungen: SQL knowledgeStarRocks basic understanding
Einsteigerfreundlichkeit: 50