MySQL的 - 有條件加入了列

Question

我有以下查詢：

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 

，我也有這樣的一個：

正如你所看到的查詢是幾乎除了同一個額外的join聲明。 兩個查詢返回我，我需要正確的價值觀，但我需要他們一起在一個單一的表，所以我這樣做：

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 

或者換句話說，我加入了第一個查詢與第二個作爲子查詢。結果集很好而且正確，但花費的時間太長，所以我在這個查詢正在運行的另一個系統中出現超時。 每個查詢獨立運行速度快，但加入他們是太慢我的需求...

我想知道是否有一種方法來優化這個，我想如果有一些聯合條件語句或某事。我搜索了信息，但我沒有任何運氣。 我在想像這樣的東西：

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 

或類似的東西。請問一些身體可以幫我嗎？我怎樣才能優化這個？ 感謝

Answer 1

你可以使用一個外部連接來計算sf_visit_file_time和一個case語句嗎？很明顯，我沒有本地模式，但類似於：

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

如果這兩個查詢是速度快，很好地工作，你只需要在一個表中的結果，你可以使用一個聯盟選擇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

在這種情況下，你是「有條件加入」被告訴你「如果我在另一張表中找到記錄，這意味着訪問完成。」

爲了創造「條件」您可以使用LEFT OUTER JOIN，而不是一個INNER JOIN

的OUTER JOIN，而不是一個INNER JOIN如果記錄在表中找到，而不是其他不破。它仍然會返回記錄。有LEFT和RIGHT外連接。你應該自己研究它們。但基本上，以達到你想要什麼，你可以做這樣的事情：

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，現在，DoneVisits將永遠存在 - 它只是爲零時，有沒有sf_visit_file_time記錄它。

Answer 4

這兩個查詢都乾淨而高效。所以，只需將它們連接在一起進行演示，將它們當作子查詢處理。

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 

這使得一個更大的查詢，但它應該在你有兩個查詢的時間之和運行。您可以將ORDER BY子句保留在子查詢中。

因此，它看起來像這樣......一個真正的查詢俱樂部三明治。

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