大量的left join 怎么优化select a.id,a.num,b.num,b.pcs,c.num,c.pcs,d.num,d.pcs,e.num,e.pcs,a.x,a.y from a left join b.id=a.id and b.time=a.timeleft join c.id=a.id and b.time=a.timeleft join d.id=a.id and b.time=a.timeleft join e.id=a.id and b.t

来源：学生作业帮助网编辑：作业帮时间：2024/10/01 21:56:57

x��R�n�@��1�}%�[|KCQڗʁ$6�*-P�%�V�)Cp�3;��]��8��d��3�;g'��Bw��瓸��e^ĒV4��9.�Y��b�s��+<|Sb�))�(�(�)�)��}��W��Yec ��_ 7I��UQDH��>�<�� O��.�b��+��r��:��+�?��\srEy�/�e�'v��턟o�w��[4��q{�[=Ǽ�mi��SC��:�cP۠�v枷pAw�6��8�rW�c}��eX��5n�U=�,_v�0�ornm�=��]��E$��F�z�ޟ �q��M+�L��+XTXG)!�#.�t��[��r8D��ǽH�� Э�^�]_w�(�0��L�n�0p:%�<��p~�n6H$��nC�fF��&n��us_ȵ:��ۅ�MH��VК��*��+��#��z�r�m��I�}=.�x�e��Fr}��N��EB��z��l�

大量的left join 怎么优化select a.id,a.num,b.num,b.pcs,c.num,c.pcs,d.num,d.pcs,e.num,e.pcs,a.x,a.y from a left join b.id=a.id and b.time=a.timeleft join c.id=a.id and b.time=a.timeleft join d.id=a.id and b.time=a.timeleft join e.id=a.id and b.t
大量的left join 怎么优化
select a.id,
a.num,
b.num,
b.pcs,
c.num,
c.pcs,
d.num,
d.pcs,
e.num,
e.pcs,
a.x,
a.y from a left join b.id=a.id and b.time=a.time
left join c.id=a.id and b.time=a.time
left join d.id=a.id and b.time=a.time
left join e.id=a.id and b.time=a.time
where a.time='2013-10-1'
这样查询效率很低,要几十分钟才能出laugh数据~每张表有上千万条数据,求问该如何优化?

大量的left join 怎么优化select a.id,a.num,b.num,b.pcs,c.num,c.pcs,d.num,d.pcs,e.num,e.pcs,a.x,a.y from a left join b.id=a.id and b.time=a.timeleft join c.id=a.id and b.time=a.timeleft join d.id=a.id and b.time=a.timeleft join e.id=a.id and b.t
在各个表的id和time属性上创建索引,而且把其中除了第一次left join中的 b.time=a.time外,其余的 b.time=a.time去掉,并先对b表执行 b.time='2013-10-1'的查询.
如果各表都需要判断时间的话,那么请先在各表上执行基于时间的选择操作,在参加左外连接.因此,时间字段上的索引很重要.

大量的left join 怎么优化select a.id,a.num,b.num,b.pcs,c.num,c.pcs,d.num,d.pcs,e.num,e.pcs,a.x,a.y from a left join b.id=a.id and b.time=a.timeleft join c.id=a.id and b.time=a.timeleft join d.id=a.id and b.time=a.timeleft join e.id=a.id and b.t left join 优化如图.左边是我查出来的.用哪种可以查出来右边的哪种结构. 删除怎么用left join inner join和left join的区别 left join和inner join的区别 left join 和 left outer join 的区别 left join 和 left outer join 的区别 left join 和 left outer join 的区别 SQL中 inner join、 left join 、right join、 outer join之间的区别 inner join,left join,right join,full join 的区别?最好用例子说明! sql中left join from 多个表怎么写select * from a,b,c,d LEFT JOIN e on e.id=a.id left join f on f.id=c.id现在这句是错的,怎么写才正确 join的过去式七年下同步优化里的 sql表连接查询的区别`inner join、left join、rightjoin、outer join举例说明· 数据库的问题：解释inner join,left outer join ,cross join 数据库中的left join 和left outer join有什么本质的区别? 录音笔上的sel是什么意思 linq用lambda表达式 left join 自连接怎么写 left join 和 right jion 怎么表示 LINQ