简述Mybatis的动态SQL是什么意思

1. Mybatis提供的动态SQL不同于传统的SQL拼接，可有效防止语句错误。
2. Mybatis实现动态SQL的元素有 if、choose、when、otherwise、trim、where、set、foreach

代码示例：

<select id="foo" parameterType="Blog" resultType="Blog">
    select * from t_blog where 1 = 1
    <if test="title != null">
        and title = #{title}
    </if>
    <if test="content != null">
        and content = #{content}
    </if>
    <if test="owner != null">
        and owner = #{owner}
    </if>
</select>

<select id="foo" parameterType="Blog" resultType="Blog">
    select * from t_blog where 1 = 1 
    <choose>
        <when test="title != null">
                and title = #{title}
        </when>
        <when test="content != null">
            and content = #{content}
        </when>
        <otherwise>
            and owner = "owner1"
        </otherwise>
    </choose>
</select>

<select id="bar" resultType="Blog">
    select * from t_blog where id in
    <foreach collection="array" index="index" 
        item="item" open="(" separator="," close=")">
        #{item}
    </foreach>
</select>