sql标签

1. 抽取可重用的sql片段，方便后面引用
2. sql抽取，经常将要查询的列名，或者插入用的列名抽取出来方便引用
3. include 来引用已经抽取的sql
4. include还可以自定义一些property，sql标签内就可以通过${prop}来直接使用

<select id="getEmpByBind" resultType="emp" databaseId="mysql">        <bind name="_lastName" value="'%'+name+'%'" />        select        <include refid="columns">            <property name="ok" value="abc" />        </include>        from employee where last_name like #{_lastName}    </select>    <sql id="columns">        last_name as lastName, email,id,gender,${ok}    </sql>