常用xml写法

<if test="paramId != null">
    AND u.id = #{paramId}
</if>

<if test="paramName != null and paramName != ''">
    AND u.name = #{paramName}
</if>

<if test="paramName != null and paramName.trim() != ''">
    AND u.name = #{paramName}
</if>

<if test="stateSet != null and stateSet.size() > 0">
    and u.state in
    <foreach collection="stateSet" item="item" open="(" separator="," close=")">
        #{item}
    </foreach>
</if>

-- 按顺序, 只会进第一个满足条件的when, 所有when都不满足的话, 进otherwise
<choose>
    <when test="sum == '1'.toString()">
        u.rank='第一名'
    </when>
    <when test="sum == '2'.toString()">
        u.rank='第二名'
    </when>
    <when test="sum == '3'.toString()">
        u.rank='第三名'
    </when>
    <otherwise>
        u.rank='路人'
    </otherwise>
</choose>

u.`name` like CONCAT(#{paramName}, '%')

<if test="gender != null gender.name() == 'MALE'">
    AND u.gender = 1
</if>