开始

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生产环境中数量
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先来写sql语句

涉及到这两张表的关联
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等待，待评价的订单。
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  1. select 
  2. count(1)
  3. from
  4. orders o
  5. left join
  6. order_status os
  8. on
  9.  o.id=os.order_id
  10. where
  11. o.user_id='21011270605KYX8H'
  12. and os.order_status=40
  13. and o.is_comment=0

状态改成10，然后下面是否评论注释掉。查询到3条数据
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select 
count(1)
from
orders o
left join
order_status os

on
 o.id=os.order_id
where
o.user_id='21011270605KYX8H'
and os.order_status=10

SQL 查找是否“存在“，别再 count 了，很耗费时间的！
https://my.oschina.net/u/4192546/blog/4964639

后端

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xml内写sql
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直接返回int
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 <select id="queryMyOrderStatusCounts" parameterType="Map" resultType="int">
    select
    count(1)
    from
    orders o
    left join
    order_status os
    on
     o.id=os.order_id
    where
    o.user_id=#{paramsMap.userId}
    and os.order_status=#{paramsMap.orderStatus}
    <if test="paramsMap.isComment != null">
      and o.is_comment=#{paramsMap.isComment}
    </if>

定义接口
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public int queryMyOrderStatusCounts(@Param("paramsMap") Map<String,Object> map);

结束