MySql 查询需要很长时间

Question

嗨，我正在执行一个查询来获取一些产品信息，但是发生了一些奇怪的事情，第一个查询快速返回结果集(.1272s)，但第二个查询(请注意，我刚刚添加了 1 列)需要永远完成( 28-35s)，有人知道发生了什么事吗？

查询 1

SELECT
p.partnumberp,
p.model,
p.descriptionsmall,
p.brandname,
sum(remainderint) stockint
from
inventario_dbo.inventoryindetails ind
left join purchaseorders.product p on (p.partnumberp = ind.partnumberp)
left join inventario_dbo.inventoryin ins on (ins.inventoryinid= ind.inventoryinid)
group by partnumberp, projectid

查询2

SELECT
p.partnumberp,
p.model,
p.descriptionsmall,
p.brandname,
p.descriptiondetail,
sum(remainderint) stockint
from
inventario_dbo.inventoryindetails inda
left join purchaseorders.product p on (p.partnumberp = inda.partnumberp)
left join inventario_dbo.inventoryin ins on (ins.inventoryinid= inda.inventoryinid)
group by partnumberp, projectid

Answer 1

除非使用聚合函数，否则不应按某些列进行分组，然后选择其他列。只有 p.partnumberp 和 sum(remainderint) 在这里有意义。您正在进行大量的联接和选择，然后大多数行的结果最终都会被丢弃。

您可以通过先执行内部选择，然后将其连接到其余表以获得最后几列的最终结果，从而使查询速度更快。

内部选择应如下所示:

select p.partnumberp, projectid, sum(remainderint) stockint
    from inventario_dbo.inventoryindetails ind
    left join purchaseorders.product p on (p.partnumberp = ind.partnumberp)
    left join inventario_dbo.inventoryin ins on (ins.inventoryinid = ind.inventoryinid)
    group by partnumberp, projectid

加入后:

select T1.partnumberp, T1.projectid, p2.model, p2.descriptionsmall, p2.brandname, T1.stockint
from
    (select p.partnumberp, projectid, sum(remainderint) stockint
        from inventario_dbo.inventoryindetails ind
        left join purchaseorders.product p on (p.partnumberp = ind.partnumberp)
        left join inventario_dbo.inventoryin ins on (ins.inventoryinid = ind.inventoryinid)
        group by partnumberp, projectid) T1
    left join purchaseorders.product p2 on (p2.partnumberp = T1.partnumberp)