StarRocks/starrocks

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

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#73,784 opened on May 25, 2026

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 (0 comments) (0 reactions) (0 assignees)Java (5,717 stars) (1,246 forks)batch import
good first issuetype/bug

Description

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

Tech stack
javasql
Domain
backenddatabase
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
SQL knowledgeStarRocks basic understanding
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
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.