mybatis查询树形菜单sql效率低

Question

<resultMap id="menuQuery" type="com.wlpy.common.entity.Menu">
    <id column="id" jdbcType="INTEGER" property="id" />
    <result column="parentId" jdbcType="VARCHAR" property="parentId" />
    <result column="menuName" jdbcType="VARCHAR" property="menuName" />
    <result column="url" jdbcType="VARCHAR" property="url" />
    <result column="type" jdbcType="VARCHAR" property="type" />
    <result column="perms" jdbcType="VARCHAR" property="perms" />
    <collection property="menuList" select="lowMenu" column="id" ofType="com.wlpy.common.entity.Menu">
        <id column="id" jdbcType="INTEGER" property="id" />
        <result column="parentId" jdbcType="VARCHAR" property="parentId" />
        <result column="menuName" jdbcType="VARCHAR" property="menuName" />
        <result column="url" jdbcType="VARCHAR" property="url" />
        <result column="type" jdbcType="VARCHAR" property="type" />
        <result column="perms" jdbcType="VARCHAR" property="perms" />
    </collection>
</resultMap>

<select id="findAllMenu" parameterType="java.util.Map" resultMap="menuQuery">
    SELECT
    m.id,
    m.parent_id AS parentId,
    m.menu_name AS menuName,
    m.url,
    m.type,
    m.perms
    FROM
    menu AS m
    WHERE
    m.available = 1
    AND m.parent_id = 0
</select>

<select id="lowMenu" parameterType="java.util.Map" resultMap="menuQuery">
      SELECT
      m.id,
      m.parent_id AS parentId,
      m.menu_name AS menuName,
      m.url,
      m.type,
      m.perms
      FROM
      menu AS m
      WHERE
      m.available = 1
      AND m.parent_id = #{id} 父级ID
</select>

Answer 1

我看sql也不复杂，是查询慢吗，看下索引使用情况。
执行计划：explain sql语句