pingcap/tidb

Compatible problem on `asin` with mysql

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#6,832 创建于 2018年6月13日

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component/expressiongood first issuehelp wantedpriority/P4type/compatibility

描述

Please answer these questions before submitting your issue. Thanks!

  1. What did you do? If possible, provide a recipe for reproducing the error.

  2. What did you expect to see?

mysql> select asin(-0.999999999);
+---------------------+
| asin(-0.999999999)  |
+---------------------+
| -1.5707516054359754 |
+---------------------+
1 row in set (0.00 sec)
  1. What did you see instead?
mysql> select asin(-0.999999999);
+--------------------+
| asin(-0.999999999) |
+--------------------+
| -1.570751605435964 |
+--------------------+
1 row in set (0.00 sec)
  1. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

master branch commit message: 0ab1b228c0e14f4e62d9de93028183bb1df58125

贡献者指南

技术栈
gosql
领域
database
议题类型
bug
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
3
预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。
1-3 hours
活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。
stale
清晰度议题是否清楚说明期望改动、验收标准和下一步。
clear
前置要求
Go programmingfloating point arithmetic
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
60
研究方向
Investigate the implementation of the `asin` function in TiDB's expression package (likely `expression/builtin math.go`). Compare the computed result with MySQL's output. The discrepancy suggests a precision issue in the algorithm or rounding. Check for any existing tests for `asin` and consider adjusting the computation to match MySQL's behavior.
Compatible problem on `asin` with mysql · pingcap/tidb#6832 | Good First Issue