constant propagation is wrong used for some collation.

[wjhuang2016]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t1(a char(10) collate utf8mb4_general_ci, index (a));
create table t2(a char(10) collate utf8_bin, index (a));
insert into t1 values ("a");
insert into t2 values ("A");
set names utf8 collate utf8_general_ci;
select * from t1, t2 where t1.a=t2.a and t1.a= "a";

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

mysql> select * from t1, t2 where t1.a=t2.a and t1.a= "a";
+------+------+
| a    | a    |
+------+------+
| a    | A    |
+------+------+
1 row in set (0.01 sec)

3. What did you see instead (Required)

mysql> select * from t1, t2 where t1.a=t2.a and t1.a= "a";
Empty set (0.00 sec)

4. What is your TiDB version? (Required)

4.0 - 4.0.10, 5.0 rc, master

[ti-srebot]

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Not a bug

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Bug

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1. Root Cause Analysis (RCA) (optional)

2. Symptom (optional)

3. All Trigger Conditions (optional)

4. Workaround (optional)

5. Affected versions

[v4.0.0:4.0.11],[5.0.0-rc]

6. Fixed versions

master