mybatis动态sql编写，遇到问题求解
在使用mybatis动态sql时，遇到如下问题：
select * from table a where a.project_id=#{projectid} and a.id != #{id} and a.status=3 and a.id_card = #{code} or a.unit_code = #{code}想要将其优化为：
select * from table a where a.project_id=#{projectid} and a.id != #{id} and a.status=3 and
<if test="type == 'idcard'">a.id_card = #{code}</if>
<if test="type == 'unitcode'">a.unit_code = #{code}</if>但优化后运行会报错（3种写法都会报badsql）。
解决方法
正确的写法如下：
select * from table a
<where>
a.project_id=#{projectId}
and a.id != #{id}
and a.status=3
<choose>
<when test="type == idCard">
and a.id_card = #{code}
</when>
<when test="type == unitCode">and a.unit_code = #{code}</when>
<otherwise>
</otherwise>
</choose>
</where> 
