Adding constraint for hostgroup_id >= 0 in mysql_servers

[pondix]

Resolves issue "mysql_servers.hostgroup_id must be >= 0" #1244

Verified migration of existing table:

2017-12-01 03:38:35 [INFO] Starting ProxySQL
2017-12-01 03:38:35 [INFO] Sucessfully started
2017-12-01 03:38:35 [INFO] Angel process started ProxySQL process 55585
Standard ProxySQL Cluster rev. 0.1.0702 -- ProxySQL_Cluster.cpp -- Thu Nov 30 23:48:56 2017
Standard ProxySQL Statistics rev. 1.4.1027 -- ProxySQL_Statistics.cpp -- Fri Dec  1 02:27:57 2017
Standard ProxySQL HTTP Server Handler rev. 1.4.1031 -- ProxySQL_HTTP_Server.cpp -- Fri Dec  1 02:27:57 2017
2017-12-01 03:38:35 ProxySQL_Admin.cpp:7726:disk_upgrade_mysql_servers(): [WARNING] Detected version v1.3.0 of table mysql_servers
2017-12-01 03:38:35 ProxySQL_Admin.cpp:7727:disk_upgrade_mysql_servers(): [WARNING] ONLINE UPGRADE of table mysql_servers in progress
Standard ProxySQL Admin rev. 0.2.0902 -- ProxySQL_Admin.cpp -- Fri Dec  1 03:37:21 2017
Standard MySQL Threads Handler rev. 0.2.0902 -- MySQL_Thread.cpp -- Thu Nov 30 23:48:56 2017
...

Verified data integrity and new table structure:

mysql> show create table mysql_servers\G
*************************** 1. row ***************************
       table: mysql_servers
Create Table: CREATE TABLE mysql_servers (
    hostgroup_id INT CHECK (hostgroup_id>=0) NOT NULL DEFAULT 0,
    hostname VARCHAR NOT NULL,
    port INT NOT NULL DEFAULT 3306,
    status VARCHAR CHECK (UPPER(status) IN ('ONLINE','SHUNNED','OFFLINE_SOFT', 'OFFLINE_HARD')) NOT NULL DEFAULT 'ONLINE',
    weight INT CHECK (weight >= 0) NOT NULL DEFAULT 1,
    compression INT CHECK (compression >=0 AND compression <= 102400) NOT NULL DEFAULT 0,
    max_connections INT CHECK (max_connections >=0) NOT NULL DEFAULT 1000,
    max_replication_lag INT CHECK (max_replication_lag >= 0 AND max_replication_lag <= 126144000) NOT NULL DEFAULT 0,
    use_ssl INT CHECK (use_ssl IN(0,1)) NOT NULL DEFAULT 0,
    max_latency_ms INT UNSIGNED CHECK (max_latency_ms>=0) NOT NULL DEFAULT 0,
    comment VARCHAR NOT NULL DEFAULT '',
    PRIMARY KEY (hostgroup_id, hostname, port) )
1 row in set (0.00 sec)

mysql> select * from mysql_servers;
+--------------+-----------+------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
| hostgroup_id | hostname  | port | status | weight | compression | max_connections | max_replication_lag | use_ssl | max_latency_ms | comment |
+--------------+-----------+------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
| 10           | 127.0.0.1 | 3306 | ONLINE | 1      | 0           | 1000            | 0                   | 0       | 0              |         |
+--------------+-----------+------+--------+--------+-------------+-----------------+---------------------+---------+----------------+---------+
1 row in set (0.00 sec)