TiDB allows variables and parameters in VIEWs while MySQL does not

[mjonss]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create view sql_mode_view as select @@sql_mode;

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

mysql> create view sql_mode_view as select @@sql_mode;
ERROR 1351 (HY000): View's SELECT contains a variable or parameter

3. What did you see instead (Required)

tidb> create view sql_mode_view as select @@sql_mode;
Query OK, 0 rows affected (0.09 sec)

4. What is your TiDB version? (Required)

tidb_version(): Release Version: v8.0.0
Edition: Community
Git Commit Hash: 8ba1fa452b1ccdbfb85879ea94b9254aabba2916
Git Branch: HEAD
UTC Build Time: 2024-03-28 14:22:34
GoVersion: go1.21.6
Race Enabled: false
Check Table Before Drop: false
Store: tikv