Default value as an expression really only supports default value as function

[morgo]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

From the MySQL manual there is an example that uses a literal default specified as an expression:

CREATE TABLE t2 (b BLOB DEFAULT ('abc'));

In my actual application, I have a similar example where the literal is '0'. If you test in MySQL you can also use expressions like DEFAULT(NOW()+2), but these are also parse errors in TiDB.

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

mysql> CREATE TABLE t2 (b BLOB DEFAULT ('abc'));
Query OK, 0 rows affected (0.03 sec)

mysql> SELECT version();
+-----------+
| version() |
+-----------+
| 8.0.32    |
+-----------+
1 row in set (0.01 sec)

3. What did you see instead (Required)

mysql> CREATE TABLE t2 (b BLOB DEFAULT ('abc'));
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your TiDB version for the right syntax to use line 1 column 38 near "'abc'))"

4. What is your TiDB version? (Required)

mysql> SELECT tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v8.2.0-alpha-602-g9794156596
Edition: Community
Git Commit Hash: 9794156596b1bbd1270f7776fb5bcad59267c25d
Git Branch: HEAD
UTC Build Time: 2024-07-17 02:29:36
GoVersion: go1.21.10
Race Enabled: false
Check Table Before Drop: false
Store: tikv
1 row in set (0.00 sec)