Vitess does not like parenthesis around selects

[Topographic0cean]

#5737 ## Overview of the Issue

We are evaluating using Vitess with our existing application. We simply put Vitess in front of our mysql 5.6 db and directed the app to Vitess with no sharding. We have seen a couple of queries fail with syntax errors that we were not expecting. If they are documented, we could not find them. The first is when there are extra parenthesis around the select. Here is vtexplain with a simplified example:

if I remove the parenthesis, vitess is happy. Note that mysql is happy with either. You may argue that the parens are not needed in this case, but we were wondering why vitess fails.

Reproduction Steps

Steps to reproduce this issue, example:

1. Deploy the following vschema which is basically empty:

{
"mainkeyspace": {
"sharded": false,
"vindexes": {
"hash": {
"type": "hash"
},
"md5": {
"type": "unicode_loose_md5",
"params": {},
"owner": ""
},
"users_name_idx": {
"type": "lookup_hash",
"params": {
"from": "name",
"table": "users_name_idx",
"to": "user_id"
},
"owner": "users"
}
},
"tables": {
}
}
}
```

2. Deploy the following schema:

CREATE TABLE notification (
name varchar(255) DEFAULT NULL,
sys_created_on datetime DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
```

3. Run vtexplain
   vtexplain -sql-file stmt.sql -schema-file schema.sql -vschema-file vschema.json

4. View error
   ERROR: vtexplain execute error in '(SELECT notification.name, notification.sys_created_on AS order FROM notification WHERE notification.sys_created_on >= '2020-04-24') ORDER BY order': syntax error at position 147 near 'ORDER'

5. Show non-error case
   If we remove the extra parens, it works:
   vtexplain -sql-file stmt.sql -schema-file schema.sql -vschema-file vschema.json

---

SELECT notification.name, notification.sys_created_on AS order FROM notification WHERE notification.sys_created_on >= '2020-04-24' ORDER BY order

1 mainkeyspace/-: select notification.name, notification.sys_created_on as order from notification where notification.sys_created_on >= '2020-04-24' order by order asc limit 10001

---

Operating system and Environment details

We are testing this on a Mac OSX Catalina (10.15.5) as that is our development environment.

[harshit-gangal]

PR: #6342 fixes this issue