MyCAT自增字段和返回生成的主键ID的经验分享
说明：
1、mysql本身对非自增长主键，使用last_insert_id()是不会返回结果的，只会返回0.
2、mysql只会对定义自增长主键，可以用last_insert_id()返回主键值。
mycat目前提供了自增长主键功能，但是如果对应的mysql节点上数据表，没有定义auto_increment，
那么在mycat层调用last_insert_id()也是不会返回结果的。
正确使用方式如下：
1、mysql定义自增主键
CREATE TABLE `tt2` (
`id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
`nm` INT(10) UNSIGNED NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MYISAM AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
2、mycat定义自增
[root@test conf]# vim schema.xml
<?xml version="1.0"?>
<!DOCTYPE mycat:schema SYSTEM "schema.dtd">
<mycat:schema xmlns:mycat="http://org.opencloudb/">
<schema name="TESTDB" checkSQLschema="false" sqlMaxLimit="100">
<!-- random sharding using mod sharind rule -->
<!-- autoIncrement="true" 属性-->
<table name="tt2" primaryKey="id" autoIncrement="true" dataNode="dn1,dn2,dn3,dn4,dn5" rule="mod-long" />
<table name="mycat_sequence" primaryKey="name" dataNode="dn1"/>
</schema>
<dataNode name="dn1" dataHost="localhost1" database="db1" />
<dataNode name="dn2" dataHost="localhost1" database="db2" />
<dataNode name="dn3" dataHost="localhost1" database="db3" />
<dataNode name="dn4" dataHost="localhost1" database="db4" />
<dataNode name="dn5" dataHost="localhost1" database="db5" />
<dataHost name="localhost1" maxCon="1000" minCon="20" balance="0" writeType="0" dbType="mysql" dbDriver="native">
<heartbeat>select user()</heartbeat>
<writeHost host="hostM1" url="127.0.0.1:3366" user="root" password="123456">
</writeHost>
</dataHost>
</mycat:schema>
3、mycat对应sequence_db_conf.properties增加相应设置；
4、mycat的对应mycat_sequence增加对应记录。
5、链接mycat，测试结果如下：
127.0.0.1/root:[TESTDB> insert into tt2(nm) values (99);
Query OK, 1 row affected (0.14 sec)
127.0.0.1/root:[TESTDB> select last_insert_id();
+------------------+
| LAST_INSERT_ID() |
+------------------+
| 101 |
+------------------+
1 row in set (0.01 sec)
127.0.0.1/root:[TESTDB> insert into tt2(nm) values (99);
Query OK, 1 row affected (0.00 sec)
127.0.0.1/root:[TESTDB> select last_insert_id();
+------------------+
| LAST_INSERT_ID() |
+------------------+
| 102 |
+------------------+
1 row in set (0.00 sec)
127.0.0.1/root:[TESTDB> insert into tt2(nm) values (99);
Query OK, 1 row affected (0.00 sec)
127.0.0.1/root:[TESTDB> select last_insert_id();
+------------------+
| LAST_INSERT_ID() |
+------------------+
| 103 |
+------------------+
1 row in set (0.00 sec)
127.0.0.1/root:[TESTDB> insert into tt2(nm) values (99);
Query OK, 1 row affected (0.01 sec)
127.0.0.1/root:[TESTDB> select last_insert_id();
+------------------+
| LAST_INSERT_ID() |
+------------------+
| 104 |
+------------------+
1 row in set (0.00 sec)
127.0.0.1/root:[TESTDB> insert into tt2(nm) values (99);
Query OK, 1 row affected (0.00 sec)
127.0.0.1/root:[TESTDB> select last_insert_id();
+------------------+
| LAST_INSERT_ID() |
+------------------+
| 105 |
+------------------+
1 row in set (0.00 sec)
127.0.0.1/root:[TESTDB> insert into tt2(nm) values (99);
Query OK, 1 row affected (0.00 sec)
127.0.0.1/root:[TESTDB> select last_insert_id();
+------------------+
| LAST_INSERT_ID() |
+------------------+
| 106 |
+------------------+
1 row in set (0.00 sec)