一、if标签

<select id="selectByMoney" resultType="demo.entity.User">
    select * from t_user
    <where>
        <if test="money != null and money != ''">
            and money>1000
        </if>
    </where>
</select>

二、foreach标签

<select id="selectUserByIds" resultType="demo.entity.User">
    select * from t_user
    <where>
        <foreach collection="ids" open="and id in(" item="id" separator="," close=")">
            #{id}
        </foreach>
    </where>
</select>

三、sql标签

<sql id="sql_temp">
    select id ,user_name, passwd, money from t_user
</sql>

<select id="login" resultType="demo.entity.User">
    <include refid="sql_temp"></include> where user_name=#{userName} and passwd=#{passwd}
</select>