from_unixtime + union all returns truncated result

[wjhuang2016]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Refer to https://asktug.com/t/topic/37509

CREATE TABLE t_a (
id int(10) unsigned NOT NULL AUTO_INCREMENT,
type tinyint(4) NOT NULL,
create_time int(11) NOT NULL,
PRIMARY KEY (id)
)

select * from t_a

id    type  create_time  
 1       1     1601004020
 2       1     1598412094
 3       1     1598498511
 4       2     1598584933
 5       3     1599794551
 6       3     1599880969

select from_unixtime(create_time,'%Y-%m-%d') as t_day,count(*) as cnt
from t_a
where `type` = 1
group by t_day
union all
select from_unixtime(create_time,'%Y-%m-%d') as t_day,count(*) as cnt
from t_a
where `type` = 3
group by t_day

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

3. What did you see instead (Required)

t_day cnt
2020-09- 1
2020-09- 1
2020-09- 1
2020-08- 1
2020-08- 1

4. What is your TiDB version? (Required)

4.0.5 master

[sre-bot]

Integrity check:
RCA symptom trigger_condition affect_version fix_version fields are empty

Please comment /info to get template

[ti-srebot]

Please edit this comment to complete the following information

Not a bug

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Bug

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Example for how to fill out the template: #20100

1. Root Cause Analysis (RCA)

For from_unixtime, Flen is set to the length of the second argument, which is wrong.

2. Symptom

Wrong result.

3. All Trigger Conditions

from_unixtime(), union all.

4. Workaround (optional)

5. Affected versions

[:v4.0.7]

6. Fixed versions

v4.0.8