MySQL的 - 有条件加入了列

Question

我有以下查询：

select ad_st_id_state, count(distinct id_visit) as Visits 
from sf_visit 
join vr_users on vi_us_id_user = sus_us_id_user 
join sf_pdv on vi_pdv_id_pdv = id_pdv 
join sf_address on pdv_ad_id_address = id_address 

group by ad_st_id_state 
order by ad_st_id_state 

，我也有这样的一个：

正如你所看到的查询是几乎除了同一个额外的join声明。 两个查询返回我，我需要正确的价值观，但我需要他们一起在一个单一的表，所以我这样做：

select fffuuu.ad_st_id_state, count(distinct id_visit) as Visitas, fffuuu.doneVisits 
from sf_visit 
join vr_users on vi_us_id_user = sus_us_id_user 
join sf_pdv on vi_pdv_id_pdv = id_pdv 
join sf_address on pdv_ad_id_address = id_address 

join (
select ad_st_id_state, count(distinct id_visit) as doneVisits 
from sf_visit 
join vr_users on vi_us_id_user = sus_us_id_user 
join sf_pdv on vi_pdv_id_pdv = id_pdv 
join sf_address on pdv_ad_id_address = id_address 
join sf_visit_file_time on id_visit = vft_vi_id_visit 

group by ad_st_id_state 
order by ad_st_id_state 
) as fffuuu on sf_address.ad_st_id_state = fffuuu.ad_st_id_state 

group by ad_st_id_state 
order by ad_st_id_state 

或者换句话说，我加入了第一个查询与第二个作为子查询。结果集很好而且正确，但花费的时间太长，所以我在这个查询正在运行的另一个系统中出现超时。 每个查询独立运行速度快，但加入他们是太慢我的需求...

我想知道是否有一种方法来优化这个，我想如果有一些联合条件语句或某事。我搜索了信息，但我没有任何运气。 我在想像这样的东西：

select ad_st_id_state, count(distinct id_visit) as Visits, if(@someVariable := true) as DoneVisits 
from sf_visit 
join vr_users on vi_us_id_user = sus_us_id_user 
join sf_pdv on vi_pdv_id_pdv = id_pdv 
join sf_address on pdv_ad_id_address = id_address 
if (@someVariable == true) then join sf_visit_file_time on id_visit = vft_vi_id_visit 

group by ad_st_id_state 
order by ad_st_id_state 

或类似的东西。请问一些身体可以帮我吗？我怎样才能优化这个？ 感谢

Answer 1

你可以使用一个外部连接来计算sf_visit_file_time和一个case语句吗？很明显，我没有本地模式，但类似于：

select ad_st_id_state, 
    count(distinct id_visit) as Visits, 
    count(distinct case when vft_vi_id_visit is not null then id_visit end) as DoneVisits 
from sf_visit 
join vr_users on vi_us_id_user = sus_us_id_user 
join sf_pdv on vi_pdv_id_pdv = id_pdv 
join sf_address on pdv_ad_id_address = id_address 
left join sf_visit_file_time on id_visit = vft_vi_id_visit 
group by ad_st_id_state 
order by ad_st_id_state 

Answer 2

如果这两个查询是速度快，很好地工作，你只需要在一个表中的结果，你可以使用一个联盟选择http://dev.mysql.com/doc/refman/5.0/en/union.html

select ad_st_id_state, count(distinct id_visit) as Visits, '' as DoneVisits 
from sf_visit 
join vr_users on vi_us_id_user = sus_us_id_user 
join sf_pdv on vi_pdv_id_pdv = id_pdv 
join sf_address on pdv_ad_id_address = id_address 
group by ad_st_id_state 
UNION 
select ad_st_id_state, '' as Visits, count(distinct id_visit) as DoneVisits 
from sf_visit 
join vr_users on vi_us_id_user = sus_us_id_user 
join sf_pdv on vi_pdv_id_pdv = id_pdv 
join sf_address on pdv_ad_id_address = id_address 
join sf_visit_file_time on id_visit = vft_vi_id_visit /* Another join has been added */ 
group by ad_st_id_state 
order by ad_st_id_state 

Answer 3

在这种情况下，你是“有条件加入”被告诉你“如果我在另一张表中找到记录，这意味着访问完成。”

为了创造“条件”您可以使用LEFT OUTER JOIN，而不是一个INNER JOIN

的OUTER JOIN，而不是一个INNER JOIN如果记录在表中找到，而不是其他不破。它仍然会返回记录。有LEFT和RIGHT外连接。你应该自己研究它们。但基本上，以达到你想要什么，你可以做这样的事情：

select ad_st_id_state, count(distinct vft_vi_id_visit) as DoneVisits 
from sf_visit 
join vr_users on vi_us_id_user = sus_us_id_user 
join sf_pdv on vi_pdv_id_pdv = id_pdv 
join sf_address on pdv_ad_id_address = id_address 
left outer join sf_visit_file_time on id_visit = vft_vi_id_visit /* Another join has been added */ 
group by ad_st_id_state 
order by ad_st_id_state 

所以，现在，DoneVisits将永远存在 - 它只是为零时，有没有sf_visit_file_time记录它。

Answer 4

这两个查询都干净而高效。所以，只需将它们连接在一起进行演示，将它们当作子查询处理。

SELECT a.ad_st_id_state, a.Visits, b.DoneVisits 
    FROM (
     /* put your first query here */ 
     ) AS a 
    LEFT JOIN (
     /* put your second query here */ 
     ) AS b ON a.ad_st_id_state = b.ad_st_id_state 
ORDER BY a.ad_st_id_state 

这使得一个更大的查询，但它应该在你有两个查询的时间之和运行。您可以将ORDER BY子句保留在子查询中。

因此，它看起来像这样......一个真正的查询俱乐部三明治。

SELECT a.ad_st_id_state, a.Visits, b.DoneVisits 
    FROM (
      select ad_st_id_state, count(distinct id_visit) as Visits 
      from sf_visit 
      join vr_users on vi_us_id_user = sus_us_id_user 
      join sf_pdv on vi_pdv_id_pdv = id_pdv 
      join sf_address on pdv_ad_id_address = id_address 
      group by ad_st_id_state 
     ) AS a 
    LEFT JOIN (
      select ad_st_id_state, count(distinct id_visit) as DoneVisits 
      from sf_visit 
      join vr_users on vi_us_id_user = sus_us_id_user 
      join sf_pdv on vi_pdv_id_pdv = id_pdv 
      join sf_address on pdv_ad_id_address = id_address 
      join sf_visit_file_time on id_visit = vft_vi_id_visit /* Another join */ 
      group by ad_st_id_state 
     ) AS b ON a.ad_st_id_state = b.ad_st_id_state 
ORDER BY a.ad_st_id_state