Function default not supported

[jackysp]

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.

create table t1(str varchar(10) default 'def',strnull varchar(10),intg int default '10',rel double default '3.14');
select default(str), default(strnull), default(intg), default(rel) from t1;

2. What did you expect to see?

mysql> select default(str), default(strnull), default(intg), default(rel) from t1;
Empty set (0.00 sec)

3. What did you see instead?

ERROR 1105 (HY000) at line 2: UnknownType: *ast.DefaultExpr

4. What version of TiDB are you using (tidb-server -V)?

[morgo]

Confirming that I can still reproduce this:

tidb> create table t1(str varchar(10) default 'def',strnull varchar(10),intg int default '10',rel double default '3.14');
Query OK, 0 rows affected (0.01 sec)

tidb> select default(str), default(strnull), default(intg), default(rel) from t1;
ERROR 1105 (HY000): UnknownType: *ast.DefaultExpr
tidb> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v2.1.0-rc.3-219-g1e0876fe8-dirty
Git Commit Hash: 1e0876fe810a832721aac52275dd2b7792fd2892
Git Branch: flush
UTC Build Time: 2018-11-24 01:12:47
GoVersion: go version go1.11 linux/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false
1 row in set (0.00 sec)