if 元素：

判断语句 ，单条件分支判断

示例：

<if test="email != null and email != ''">
       a.email like CONCAT('%', #{email}, '%') and
</if>

Trim、where、set ：用于处理sql拼装问题

where示例：

<where>
      <if test="email != null and email != ''">
        and a.email like CONCAT('%', #{email}, '%')
      </if>
      <if test="sex != null ">
        and a.sex = #{sex}
      </if>
</where>

set示例：

<set>
      <if test="userName != null">
        user_name = #{userName,jdbcType=VARCHAR},
      </if>
      <if test="realName != null">
        real_name = #{realName,jdbcType=VARCHAR},
      </if>
      <if test="sex != null">
        sex = #{sex,jdbcType=TINYINT},
      </if>
      <if test="mobile != null">
        mobile = #{mobile,jdbcType=VARCHAR},
      </if>
      <if test="email != null">
        email = #{email,jdbcType=VARCHAR},
      </if>
      <if test="note != null">
        note = #{note,jdbcType=VARCHAR},
      </if>
      <if test="position != null">
        position_id = #{position.id,jdbcType=INTEGER},
      </if>
</set>

trim示例：（前面where和set都可以改成trim）

<trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="id != null">
        id,
      </if>
      <if test="userName != null">
        user_name,
      </if>
      <if test="realName != null">
        real_name,
      </if>
      <if test="sex != null">
        sex,
      </if>
      <if test="mobile != null">
        mobile,
      </if>
      <if test="email != null">
        email,
      </if>
      <if test="note != null">
        note,
      </if>
      <if test="position != null">
        position_id,
      </if>
</trim>

choose、when、otherwise示例：多条件分支判断

<where>
      <choose>
        <when test="email != null and email != ''">
          and a.email like CONCAT('%', #{email}, '%')
        </when>
        <when test="sex != null">
          and a.sex = #{sex}
        </when>
        <otherwise>
          and 1=1
        </otherwise>
      </choose>
</where>

 

foreach ：

在in语句等列举条件常用，常用于实现批量操作

<foreach collection="array" open="(" close=")" item="userName"
            index="i" separator=",">
            #{userName}
</foreach>