五、动态SQL（）

一、<choose><when><otherwise>

这是一套标签, 功能类似于 switch...case...

<select id="sel1" resultType="User">
        select * from tb_user
        <where>
            <choose>
                <when test="user != null and user != ''">
                    and user = #{user}
                </when>
                <when test="passwd != null and passwd != ''">
                    and passwd = #{passwd}
                </when>
                <otherwise>
                    and 1 = 1
                </otherwise>
            </choose>
        </where>
</select>