EXPORT_SET result type incompatible with MySQL lead to create index failed

[aytrack]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t1(a char, b varchar(20), c char, d varchar(20));
alter table t1 add index eidx ((export_set(3, a, c, ',', 5)));

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

mysql> alter table t1 add index eidx ((export_set(3, a, c, ',', 5)));
Query OK, 0 rows affected (0.05 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SELECT EXPORT_SET(5,'Y','N',',',4);
Field   1:  `EXPORT_SET(5,'Y','N',',',4)`
Catalog:    `def`
Database:   ``
Table:      ``
Org_table:  ``
Type:       VAR_STRING
Collation:  utf8mb4_general_ci (45)
Length:     508
Max_length: 7
Decimals:   31
Flags:

3. What did you see instead (Required)

mysql> alter table t1 add index eidx ((export_set(3, a, c, ',', 5)));
ERROR 1170 (42000): BLOB/TEXT column '_V$_eidx_0' used in key specification without a key length

mysql> SELECT EXPORT_SET(5,'Y','N',',',4);
Field   1:  `EXPORT_SET(5,'Y','N',',',4)`
Catalog:    `def`
Database:   ``
Table:      ``
Org_table:  ``
Type:       LONG_BLOB
Collation:  utf8mb4_bin (46)
Length:     67108864
Max_length: 7
Decimals:   31
Flags:      NOT_NULL

4. What is your TiDB version? (Required)

| tidb_version()                                                                                                                                                                                                                                                                                                       |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v5.2.0
Edition: Community
Git Commit Hash: 88f60fe1140de999c2e64ca56edffb7db7393f1e
Git Branch: heads/refs/tags/v5.2.0
UTC Build Time: 2021-08-13 15:08:56
GoVersion: go1.16.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |

[aytrack]

from_base64、repeat、substring、mid、right、left、substr has the same problem

[ti-srebot]

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