Incorrect unix_timestamp result when utc time can be mapped to multi time in one zone

[xzhangxian1008]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

set time_zone="Europe/Vilnius";
select unix_timestamp("2020-10-25 3:45");

2. What did you expect to see? (Required)

mysql> select unix_timestamp("2020-10-25 3:45"); 
+-----------------------------------+
| unix_timestamp("2020-10-25 3:45") |
+-----------------------------------+
|                        1603586700 |
+-----------------------------------+

3. What did you see instead (Required)

mysql> select unix_timestamp("2020-10-25 3:45");
+-----------------------------------+
| unix_timestamp("2020-10-25 3:45") |
+-----------------------------------+
|                        1603590300 |
+-----------------------------------+

Returned time should be another mapped time.

4. What is your TiDB version? (Required)

nightly(fc8bdb5)

[Defined2014]

I asked ChatGPT seems the result in TiDB is correct.

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What is the Unix timestamp corresponding to 2020-10-25 03:45 in Vilnius, Lithuania?

On October 25, 2020, Lithuania (Vilnius) switched from Daylight Saving Time (EEST, UTC+3) to Standard Time (EET, UTC+2). The time change occurred at 03:00 local time, meaning the clock was set back from 03:00 to 02:00.

Key Question:

At 03:45 local time, was it still in Daylight Saving Time (UTC+3) or had it already switched to Standard Time (UTC+2)?

• If it was still in DST (EEST, UTC+3) → The corresponding UTC time would be 2020-10-25 00:45.
• If it was already in Standard Time (EET, UTC+2) → The corresponding UTC time would be 2020-10-25 01:45.

Now, calculating the Unix timestamps:

• Unix timestamp 1 (UTC 00:45) → 1603586700
• Unix timestamp 2 (UTC 01:45) → 1603590300

Since the time change occurred at 03:00, by 03:45, the region was already in Standard Time (EET, UTC+2).
Thus, the most likely Unix timestamp for 2020-10-25 03:45 (Vilnius time) is 1603590300.

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What were the times before and after the time change?

On October 25, 2020, at 03:00 local time, Lithuania (Vilnius) switched from Daylight Saving Time (EEST, UTC+3) to Standard Time (EET, UTC+2). This meant that the clock was set back from 03:00 to 02:00. Below is the corresponding Unix timestamp information before and after the transition:

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Before the transition (Daylight Saving Time, UTC+3)

Lithuania Time (EEST)	UTC Time	Unix Timestamp
2020-10-25 01:59:59	2020-10-24 22:59:59 UTC	1603576799
2020-10-25 02:00:00	2020-10-24 23:00:00 UTC	1603576800
2020-10-25 02:59:59	2020-10-24 23:59:59 UTC	1603580399
2020-10-25 03:00:00	2020-10-25 00:00:00 UTC	1603580400
(At this point, the clock is set back to 02:00:00 EET.)

---

Summary

• Before 03:00 (EEST, UTC+3), the time followed UTC+3.
• After 03:00 (EET, UTC+2), the time followed UTC+2.
• The local time 02:00 - 02:59 appeared twice (once in DST and once in standard time).
• Unix timestamps remained continuous and did not repeat, but local time between 02:00 - 02:59 had two different meanings, depending on whether it was before or after the transition.