pingcap/tidb

Float precision is different from MySQL

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#11,328 opened on 2019年7月18日

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説明

Description

Bug Report

When insert into float column, the data precision is not consistent with mysql.

The mysql default float precision is 6 and tidb is 8.

  1. What did you do?
create table t (t float);
insert into t values(0.12345678912345);
  1. What did you expect to see? In Mysql 5.7
mysql> select * from t;
+----------+
| t        |
+----------+
| 0.123457 |
+----------+
  1. What did you see instead?

In TiDB v3.0.0

tidb> select * from t;
+------------+
| t          |
+------------+
| 0.12345679 |
+------------+
  1. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?
tidb> select tidb_version();
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                                                              |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v3.0.0
Git Commit Hash: 60965b006877ca7234adaced7890d7b029ed1306
Git Branch: HEAD
UTC Build Time: 2019-06-28 12:14:07
GoVersion: go version go1.12 linux/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

SIG slack channel

#sig-exec

Score

300

Mentor

  • @lzmhhh123

コントリビューターガイド

技術スタック
gosql
領域
database
Issue 種別
bug
難度新しい貢献者にとっての実装難度です。1 は非常に小さな変更、5 は専門的な作業です。
3
推定時間経験ある貢献者が調査、実装、テスト、pull request 準備にかけるおおよその時間範囲です。
1-2 days
活動状況Issue が今どれだけ取り組みやすいかを示します。新しい、活発、古い、ブロック中、またはメンテナー入力待ちなどです。
stale
明確さ期待される変更、受け入れ条件、次の手順がどれだけ明確かを示します。
mostly clear
前提条件
GoSQLfloat precision
初心者向け度初回貢献者にどれだけ取り組みやすいかを 1-100 で推定したスコアです。
60
調査方針
Investigate how TiDB handles float data type precision. The issue indicates that MySQL default float precision is 6, while TiDB uses 8. Look into the type system, specifically in expressions or type inference, to find where the precision is set. Relevant files might be in the types package or during table creation. Check comments in the issue for any hints from the mentor @lzmhhh123.
Float precision is different from MySQL · pingcap/tidb#11328 | Good First Issue