pingcap/tidb

zeroDate behavior for date_add and timestampdiff is not consistent in tidb

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#15,234 opened on Mar 9, 2020

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Description

Description

Bug Report

Please answer these questions before submitting your issue. Thanks!

  1. What did you do?
mysql> select timestampdiff(day,'0000-00-00 00:00:00','2020-01-01 00:00:00');
+----------------------------------------------------------------+
| timestampdiff(day,'0000-00-00 00:00:00','2020-01-01 00:00:00') |
+----------------------------------------------------------------+
|                                                           NULL |
+----------------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> select date_add('0000-00-00 00:00:00', interval 2020 year);
+-----------------------------------------------------+
| date_add('0000-00-00 00:00:00', interval 2020 year) |
+-----------------------------------------------------+
| 2019-11-30 00:00:00                                 |
+-----------------------------------------------------+
1 row in set, 1 warning (0.00 sec)

  1. What did you expect to see? timestampdiff and date_add should both return NULL or meaningful result. BTW in mysql both timestampdiff and date_add return NULL

  2. What did you see instead?

mysql> select timestampdiff(day,'0000-00-00 00:00:00','2020-01-01 00:00:00');
+----------------------------------------------------------------+
| timestampdiff(day,'0000-00-00 00:00:00','2020-01-01 00:00:00') |
+----------------------------------------------------------------+
|                                                           NULL |
+----------------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> select date_add('0000-00-00 00:00:00', interval 2020 year);
+-----------------------------------------------------+
| date_add('0000-00-00 00:00:00', interval 2020 year) |
+-----------------------------------------------------+
| 2019-11-30 00:00:00                                 |
+-----------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
  1. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

tidb master

Contributor guide

Tech stack
gomysql
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.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Go programmingTiDB source code navigationMySQL SQL syntax
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65
Research direction
Look for the implementation of 'date add' and 'timestampdiff' functions in the TiDB source code, likely under the 'expression' or 'time' package. Check how zero dates (0000-00-00) are handled. The expected behavior is to return NULL for invalid dates, as MySQL does. Compare with MySQL's handling. The fix should ensure consistent NULL return for zero dates in both functions.