mybatis 动态元素

动态SQL是MyBatis最强大的特性之一。用于实现动态SQL的主要元素如下：  
1、where、if  
2、choose、when、otherwise  
3、set、trim  

4、foreach

1、where、if	<select id="getEmpByIf" resultType="Emp" parameterType="Emp">     select * from emp     <where>         <if test="job != null and job != ''">             and job = #{job}         </if>     </where> </select>
2、choose、when、otherwise	<select id="getEmpByChoose" resultType="Emp" parameterType="Emp">     select * from emp where 1 = 1     <choose>         <when test="job != null">             and job = #{job}         </when>         <when test="deptno != null">             and deptno = #{deptno}         </when>         <otherwise>              and mgr = #{mgr}         </otherwise>     </choose> </select>
3、set、trim
4.1、foreach:参数数组
4.2、foreach:参数List

整理自：https://blog.youkuaiyun.com/qq_32588349/article/details/51541871