Regexp should report error when pattern parameter is empty string

[yibin87]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

mysql> create table t0 (a varchar(10));
mysql> insert into t0 values('');
mysql> select 'hello' regexp a from t0;

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

Error "Empty pattern is invalid" should be reported

3. What did you see instead (Required)

mysql> select 'hello' regexp a from t0;
+------------------+
| 'hello' regexp a |
+------------------+
|                1 |
+------------------+
1 row in set (0.01 sec)

4. What is your TiDB version? (Required)

---------------------------------------------------------------------------------------+
| Release Version: v8.2.0-alpha-6-g8f138d5113
Edition: Community
Git Commit Hash: 8f138d5
Git Branch: HEAD
UTC Build Time: 2024-04-22 08:00:01
GoVersion: go1.21.6
Race Enabled: false
Check Table Before Drop: false
Store: tikv |

[yibin87]

/sig execution

[yibin87]

/severity minor

[yibin87]

/label affects-8.1

[yibin87]

/assign @yibin87