mysql关联查询出现的数据不准确问题

主要还是自己对sql语句的掌握程度太低了,还需要多多加强sql语句编写,最初我的语句是这样写的:



//sql片段
 
        and orders.uid = #{ouid}
        
            and orders.state = #{ostate}
        
    

也是无意间发现数据不准确,起初还没发现问题所在。。。。。

后来改了下sql:




//sql片段
 
        and orders.uid = #{ouid}
        
            and orders.state = #{ostate}
        
    

想实现的功能是订单的分页,每页显示12条订单数据

最初的写法导致了我每页显示的数据个数都不统一,多少个都有可能,但是我的分页算法是指明了的每页显示12条数据,这也是我发现问题的原因。。。
分析:
1,因为最初的写法是将所有的表进行关联了,关联查询后我进行了limit ,这时的关联查询会查出很多结果,毕竟订单下有订单项,订单项下有商品,商品下还要对应多张图片,。。。此时我进行的截取肯定也是查询出了这么多的结果集之后进行的,这时候在取12条数据也就是几个订单的结果,肯定不会是12个订单的结果了,x下面展示的是将最初的语句查询结果

最初的查询语句:

 select     orders.aid as oaid ,orders.date as odate,orders.oid,orders.order_number,orders.state as ostate,
                    orders.total, orders.uid as ouid,
                    address.addr,address.aid,address.code,address.date as addrdate ,address.`name` as addrname,
                    address.province,address.region,address.state as addrstate,address.tel,address.uid as addruid,
                    order_item.order_item_id,order_item.pid as oipid,
                    order_item.count,order_item.sub_total,order_item.oid as oioid,order_item.date as oidate,
                    product.pid,product.state as pstate,product.pname,product.pdesc,product.date as pdate,
                    product.csid,product.market_price,product.shop_price,product.sales,product.stock,
                    image.image_id,image.name as imgname,image.old_name,image.path,
                    image.date as imgdate,image.pid as imgpid,image.state as imgstate
                from    orders
                INNER  JOIN address
                on orders.aid = address.aid
                INNER  JOIN order_item
                on orders.oid = order_item.oid
                left join product
                on order_item.pid = product.pid
                INNER  join image
                on image.pid = product.pid
                WHERE orders.uid = 'ffef0a7cd0484739b06c8c6dd83f0c13'  and orders.state =1 limit 0 ,10
QQ截图20190104201402.png

可以看到查询出的10条结果中前三条就出现了同一个订单的情况,这时候在去封装也就是8个订单了,并不是10个订单,也就解释通了为什么前台每页最初展示的订单个数都是不同的了,如果恰巧有一个订单正好10个订单项,而且就在数据截取的第一个时,那么这页就只有这一个订单了。


下面展示一下正确的做法,因为我要查询订单,所以查询要以订单为主,先去查订单,然后在去和订单项,商品,图片什么的去关联,这时候在去查询就对了,而且这时查询出的数据不止十条,因为每个订单项中可能不仅只有一个商品。

SELECT * from
            (select  orders.aid as oaid ,orders.date as odate,orders.oid,orders.order_number,orders.state as ostate,
            orders.total, orders.uid as ouid
            from  orders
           WHERE orders.uid = 'ffef0a7cd0484739b06c8c6dd83f0c13'  and orders.state =1 
             limit 0,10) as ord
        LEFT JOIN
            (select   order_item.order_item_id,order_item.pid as oipid,
            order_item.count,order_item.sub_total,order_item.oid as oioid,order_item.date as oidate,
            product.pid,product.state as pstate,product.pname,product.pdesc,product.date as pdate,
            product.csid,product.market_price,product.shop_price,product.sales,product.stock,
            image.image_id,image.name as imgname,image.old_name,image.path,
            image.date as imgdate,image.pid as imgpid,image.state as imgstate
            from  order_item
            left join product
            on order_item.pid = product.pid
            left join image
            on image.pid = product.pid) as orderExt

            on ord.oid = orderExt.oioid
QQ截图20190104202546.png

可以看到正确的查询结果,结果一共28条订单项数据,完美!加油!!!!

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