select sum(case when a <= 0 or a > 1000 then 0.0 else b end) from t returns wrong decimal

[wjhuang2016]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t(a int primary key, b int);
insert into t values (1, 11), (4, 44), (2, 22), (3, 33);
mysql> select sum(case when a <= 0 or a > 1000 then 0.0 else b end) from t;
+-------------------------------------------------------+
| sum(case when a <= 0 or a > 1000 then 0.0 else b end) |
+-------------------------------------------------------+
|                                                   110 |
+-------------------------------------------------------+
1 row in set (0.01 sec)

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

mysql> select sum(case when a <= 0 or a > 1000 then 0.0 else b end) from t;
+-------------------------------------------------------+
| sum(case when a <= 0 or a > 1000 then 0.0 else b end) |
+-------------------------------------------------------+
|                                                 110.0 |
+-------------------------------------------------------+
1 row in set (0.01 sec)

3. What did you see instead (Required)

mysql> select sum(case when a <= 0 or a > 1000 then 0.0 else b end) from t;
+-------------------------------------------------------+
| sum(case when a <= 0 or a > 1000 then 0.0 else b end) |
+-------------------------------------------------------+
|                                                   110 |
+-------------------------------------------------------+
1 row in set (0.01 sec)

4. What is your TiDB version? (Required)

master

[time-and-fate]

/label sig/execution

[lzmhhh123]

@dyzsr PTAL.

[dyzsr]

/assign @dyzsr

[jebter]

/info

[ti-srebot]

Before closing the bug, please complete the following info

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Case Bug:

1. RCA
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2. Symptom
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3. Correct minimal reproduce step:(optional)

4. Solution(optional):
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5. W/A：
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6. Affected versions
    [Since version: End version], can be multiple collections
    If the bug only affect unreleased version, please input: unreleased
    eg:  [v3.0.1:v3.1.5],[v4.0.1:v4.0.5] or unreleased

7. Fix versions
    Release versions that will include this fix.
    If the Fix version have not been planned when the issue is closed, please input: unplanned
    eg: v4.0.5, v3.0.1 or unplanned