Support alter table rename key.

[winkyao]

create table t1 (pk int primary key, i int, j int, key a(i));
alter table t1 rename key a to b;
alter table t1 rename index b to c;

reports line 1 column 25 near " a to b;" (total length 33)

[nanne007]

rename column also report the same error.

[morgo]

Rename key works fine now. However, rename column does not. I will close this bug and create a new one:

mysql> create table t1 (pk int primary key, i int, j int, key a(i));
Query OK, 0 rows affected (0.12 sec)

mysql> alter table t1 rename key a to b;
Query OK, 0 rows affected (0.08 sec)

mysql> alter table t1 rename index b to c;
Query OK, 0 rows affected (0.10 sec)

mysql> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v3.0.0-beta.1-109-g7666f688b
Git Commit Hash: 7666f688b3d91ea84fa6b0a20c2e784fff3c8945
Git Branch: master
UTC Build Time: 2019-04-17 05:09:28
GoVersion: go version go1.12.1 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)