Support for hex & shard in vindex query

[aquarapid]

This uses #6260 as a base, see that for history.

Few things:

• Renamed hex(keyspace_id) -> hex_keyspace_id, otherwise you cannot select it as it's own column (the sql parser will think you're trying to apply a function)
• Display the hex_keyspace_id values without 0x prefixes, following the MySQL HEX() convention.
• One remaining issue (which I'm not sure we can/should solve) is that if you have a single-shard keyspace where you've initialized the shard as 0 instead of -, you will receive - back as your shard "range". You will have to then convert this back to 0 as if you want to go ahead and use it to target a shard.

As an example using our local 101_initial_cluster.sh cluster example:

• Apply the vschema to the commerce keyspace:

{
"sharded": true,
"vindexes": {
  "hash": {
    "type": "hash"
  },
  "xxhash": {
    "type": "xxhash"
  }
}
}

• Now you can query the hash and xxhash vindex:

$ mysql  -u root -P 15306 -h 127.0.0.1  -A  -c
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
.
.
.

mysql> use commerce;
Database changed

mysql> select * from hash where id = 1004\G
*************************** 1. row ***************************
           id: 1004
  keyspace_id: �>򥍮ٞ
  range_start: 
    range_end: 
hex_keyspace_id: d03ef2a58daed99e
        shard: -
1 row in set (0.00 sec)

mysql> select * from xxhash where id = 1004\G 
*************************** 1. row ***************************
           id: 1004
  keyspace_id: k�2�[�1v
  range_start: 
    range_end: 
hex_keyspace_id: 6bb432a45b8d3176
        shard: -
1 row in set (0.00 sec)

mysql> select hex_keyspace_id from xxhash where id = 1004\G
*************************** 1. row ***************************
hex_keyspace_id: 6bb432a45b8d3176
1 row in set (0.01 sec)

[harshit-gangal]

cc: #4501

[harshit-gangal]

LGTM

Any reason for keeping it in draft mode?

[aquarapid]

Only reason I left in draft was to see if anyone had an opinion/idea around the '0' vs '-' shard naming thing.

[deepthi]

Only reason I left in draft was to see if anyone had an opinion/idea around the '0' vs '-' shard naming thing.

I think that is fine for now. I can't find the reference but @sougou had stated that 0 is still around because that is how things started but - is now the canonical single shard.

[derekperkins]

This is awesome!