xy720 opened a new pull request, #64622:
URL: https://github.com/apache/doris/pull/64622
### What problem does this PR solve?
Problem Summary:
`SELECT round(23900/293, 2)` returns `81.56999999999999` instead of `81.57`.
The same problems exist in all round-like functions (round / round_bankers /
ceil / floor / truncate).
Root cause:
Round(double, n) on a double cannot land on a clean N-decimal value: 81.57
is not representable in binary, the nearest double bit pattern is
81.56999999999999488....
And the formatter "%.16g," for double it will keep 16 significant digits
(see doris 4.x docs for DOUBLE type), which faithfully prints those tail
digits.
Round-like function themselves are computing correctly, the return value
just cannot fit cleanly into a double container.
Behavior change:
Round-like functions with arguments (double, const_int >= 0) now retrun
column type DECIMAL instead of DOUBLE, matching MySQL. DOUBLE values with |x|
>= 1e15 no longer fit through the inserted cast and become NULL (or
ARITHMETIC_OVERFLOW_ERROR in strict mode); such double values already render as
scientific notation under the prior behavior, so the cost is small.
### Release note
None
### Check List (For Author)
- Test <!-- At least one of them must be included. -->
- [x] Regression test
- [x] Unit Test
- [ ] Manual test (add detailed scripts or steps below)
- [ ] No need to test or manual test. Explain why:
- [ ] This is a refactor/code format and no logic has been changed.
- [ ] Previous test can cover this change.
- [ ] No code files have been changed.
- [ ] Other reason <!-- Add your reason? -->
- Behavior changed:
- [ ] No.
- [x] Yes. <!-- Explain the behavior change -->
- Does this need documentation?
- [x] No.
- [ ] Yes. <!-- Add document PR link here. eg:
https://github.com/apache/doris-website/pull/1214 -->
### Check List (For Reviewer who merge this PR)
- [ ] Confirm the release note
- [ ] Confirm test cases
- [ ] Confirm document
- [ ] Add branch pick label <!-- Add branch pick label that this PR should
merge into -->
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