1.下载

# wget http://dl.mycat.io/1.6-RELEASE/Mycat-server-1.6-RELEASE-20161028204710-linux.tar.gz

2.安装

# tar -zxvf ~/Mycat-server-1.6-RELEASE-20161028204710-linux.tar.gz -C /usr/local

3.配置schema.xml

# cd /usr/local/mycat/conf
# vim schema.xml

<?xml version="1.0"?>
<!DOCTYPE mycat:schema SYSTEM "schema.dtd">
<mycat:schema xmlns:mycat="http://io.mycat/">
<!--schema 数据库-->

    <schema name="testMyCat" checkSQLschema="false" sqlMaxLimit="100">
<!--table 表名-->

        <table name="order"  type="global" dataNode="order" />
        <table name="orderDetail"  type="global" dataNode="orderDetail" />
        <table name="commodity"  type="global" dataNode="order" />
    </schema>
<!---datanode数据节点，database对应各个datahost中的数据库名，datahost用于配置数据库服务器地址->

    <dataNode name="order" dataHost="host2" database="jxtest" />
    <dataNode name="orderDetail" dataHost="host1" database="usercenter" />
    <dataHost name="host1" maxCon="1000" minCon="10" balance="0"
              writeType="0" dbType="mysql" dbDriver="native" switchType="1"  slaveThreshold="100">
        <heartbeat>select user()</heartbeat>
        <writeHost host="hostM1" url="192.168.3.30:3306" user="root" password="Gaia@Works12345^&amp;*()" />
    </dataHost>
    <dataHost name="host2" maxCon="1000" minCon="10" balance="0"
              writeType="0" dbType="mysql" dbDriver="native" switchType="1"  slaveThreshold="100">
        <heartbeat>select user()</heartbeat>
        <writeHost host="hostM2" url="192.168.3.62:4000" user="root" password="" />
    </dataHost>
</mycat:schema>

mycat就是把跨库的数据库表，汇集到schema（新库）中，然后就可以join查询了

4.配置server.xml

# vim server.xml       #然后找到user节点配置

<user name="root">
        <property name="password">123456</property>
        <property name="schemas">testMyCat</property>
    </user>
<!--user.name登陆用户名，password登录密码，schemas该用户可使用的数据库名，testMayCat对应schema.xml文件中配置的schema-->

5.启动mycat

# cd /usr/local/mycat/bin
# ./mycat start

6.查看mycat状态

# ./mycat status
Mycat-server is running (29287).

7.使用mysql客户端连接mycat

然后就可以使用mysql语法查询了

8. 两个表的join

/*!mycat:catlet=io.mycat.catlets.ShareJoin */
SELECT
*
FROM t_order t
INNER JOIN order_detail td ON t.orderId = td.orderId

9.三个表的join

/*!mycat:catlet=io.mycat.catlets.ShareJoin */
SELECT
*
FROM t_order t
INNER JOIN order_detail td ON t.orderId = td.orderId
INNER JOIN commodity c ON td.commodityId = c.id

可见，三个表的join，mycat是不支持的