聯盟所有查詢花費的時間太長

Question

這個問題已被多次詢問，我確定，但每種情況都不一樣。

我有一臺強大的2GB內存的計算機上安裝MySQL，它不會做太多，所以計算機就足夠了。

下面的查詢已建成爲一個觀點：

create view view_orders as 

select distinct 

    tbl_orders_order.order_date AS sort_col, 
    tbl_orders_order.order_id AS order_id, 
_utf8'website' AS src,tbl_order_users.company AS company, 
tbl_order_users.phone AS phone, 
tbl_order_users.full_name AS full_name, 
time_format(tbl_orders_order.order_date,_utf8'%H:%i') AS c_time, 
date_format(tbl_orders_order.order_date,_utf8'%d/%m/%Y') AS c_date, 
tbl_orders_order.comments AS comments, 
tbl_orders_order.tmp_cname AS tmp_cname, 
tbl_orders_order.tmp_pname AS tmp_pname, 
count(tbl_order_docfiles.docfile_id) AS number_of_files, 
(case tbl_orders_order.status when 1 then _utf8'completed' when 2 then _utf8'hc' when 0 then _utf8'not-completed' when 3 then _utf8'hc-canceled' end) AS status, 

tbl_orders_order.employee_name AS employee_name, 
tbl_orders_order.status_date AS status_date, 
tbl_orders_order.cancel_reason AS cancel_reason 

from 
     tbl_orders_order left join tbl_order_users on tbl_orders_order.user_id = tbl_order_users.user_id 
    left join 
     tbl_order_docfiles on tbl_order_docfiles.order_id = tbl_orders_order.order_id 

    group by 
     tbl_orders_order.order_id 



union all 

select distinct tbl_h.h_date AS sort_col, 
(case tbl_h.sub_oid when 0 then tbl_h.order_number else concat(tbl_h.order_number,_utf8'-',tbl_h.sub_oid) end) AS order_id, 
(case tbl_h.type when 1 then _utf8'פקס' when 2 then _utf8'email' end) AS src,_utf8'' AS company, 
_utf8'' AS phone,_utf8'' AS full_name,time_format(tbl_h.h_date,_utf8'%H:%i') AS c_time, 
date_format(tbl_h.h_date,_utf8'%d/%m/%Y') AS c_date,_utf8'' AS comments,tbl_h.client_name AS tmp_cname, 
tbl_h.project_name AS tmp_pname, 
tbl_h.quantity AS number_of_files, 
_utf8'completed' AS status, 
tbl_h.computer_name AS employee_name, 
_utf8'' AS status_date, 
_utf8'' AS cancel_reason 

from tbl_h; 

查詢中使用UNION，比我瞭解UNION ALL的文章，現在使用的是。

查詢本身需要大約3秒鐘的時間（UNION需要4.5-5.5秒） 單獨的每個部分以秒爲單位運行。

應用程序會對此視圖進行排序和選擇，這會使處理時間更長 - 查詢緩存大約6秒，如果數據更改大約12秒或更長。

我沒有看到其他方式來結合這兩個結果，因爲這兩個排序需要顯示給用戶，我猜我做的事情是錯誤的。

當然這兩個表都使用主鍵。

UPDATE !!!!

它並沒有幫助，我從聯合查詢中得到了utf8/case/date_format，並刪除了區別，現在查詢需要4秒（甚至更長）。 查詢無case/date/utf8（僅聯合）縮短爲2.3秒（0.3秒改進）。

創建視圖view_orders作爲

select *, 
    (CASE src 
     WHEN 1 THEN 
      _utf8'fax' 
     WHEN 2 THEN 
      _utf8'mail' 
     WHEN 3 THEN 
      _utf8'website' 
    END) AS src, 

    time_format(order_date,'%H:%i') AS c_time, 
    date_format(order_date,'%d/%m/%Y') AS c_date, 

    (CASE status 
     WHEN 1 THEN 
      _utf8'completed' 
     WHEN 2 THEN 
      _utf8'hc handling' 
     WHEN 0 THEN 
      _utf8'not completed' 
     WHEN 3 THEN 
      _utf8'canceled' 
    END) AS status 

FROM 
(
select 

    o.order_date AS sort_col, 
    o.order_id, 
    3 AS src, 

    u.company, 
    u.phone, 
    u.full_name, 

    o.order_date, 

    o.comments, 
    o.tmp_cname, 
    o.tmp_pname, 
    count(doc.docfile_id) AS number_of_files, 

    o.status, 

    o.employee_name, 
    o.status_date, 
    o.cancel_reason 

from 
     tbl_orders_order o 
    LEFT JOIN 
     tbl_order_users u ON u.user_id = o.user_id 
    LEFT JOIN 
     tbl_order_docfiles doc ON doc.order_id = o.order_id 

    GROUP BY 
     o.order_id 

union all 

select 

    h.h_date AS sort_col, 
    (case h.sub_oid when 0 then h.order_number else concat(h.order_number,'-',h.sub_oid) end) AS order_id, 
    h.type as src, 

    '' AS company, 
    '' AS phone, 
    '' AS full_name, 

    h.h_date, 

    '' AS comments, 
    h.client_name AS tmp_cname, 
    h.project_name AS tmp_pname, 
    h.quantity AS number_of_files, 
    1 AS status, 

    h.computer_name AS employee_name, 
    '' AS status_date, 
    '' AS cancel_reason 

from tbl_h h 

）

Answer 1

它可能與所述UNION觸發字符集轉換。例如，一個查詢中的cancel_reason被定義爲utf8，但另一個查詢中沒有指定。

檢查運行此查詢時是否有非常高的CPU峯值，這將表示轉換。

就我個人而言，我會首先完成原始數據的聯合，然後應用案例和轉換語句。但我不確定這會對錶現產生什麼影響。

Answer 2

想想你使用的UNION和DISTINCT關鍵字。你的查詢是否真的會導致重複行？如果是，刪除重複的優化查詢可能會是這種形式的：

SELECT ... -- No "DISTINCT" here 
UNION 
SELECT ... -- No "DISTINCT" here 

大概沒有必要在兩個子查詢DISTINCT。如果重複是不可能的，請嘗試使用此表單。這將是你查詢的最快執行（不進一步優化子查詢）：

SELECT ... -- No "DISTINCT" here 
UNION ALL 
SELECT ... -- No "DISTINCT" here 

理由：無論UNION和DISTINCT你的中間結果集的應用"UNIQUE SORT"操作。根據您的子查詢返回多少數據，這可能非常昂貴。這是原因之一，爲什麼忽略DISTINCT和更換UNION通過UNION ALL要快得多。

UPDATE另一個想法，如果你必須刪除重複：在內部查詢第一刪除重複和格式化日期和代碼只在外部查詢之後。這將加速"UNIQUE SORT"操作，因爲比較32/64-bit integers不是比較varchars更便宜：

SELECT a, b, date_format(c), case d when 1 then 'completed' else '...' end 
FROM (
    SELECT a, b, c, d ... -- No date format here 
    UNION 
    SELECT a, b, c, d ... -- No date format here 
) 

Answer 3

你可以試試這個：

SELECT 
    o.order_date AS sort_col, 
    o.order_id AS order_id, 
    _utf8'website' AS src, 
    u.company AS company, 
    u.phone AS phone, 
    u.full_name AS full_name, 
    time_format(o.order_date,_utf8'%H:%i') AS c_time, 
    date_format(o.order_date,_utf8'%d/%m/%Y') AS c_date, 
    o.comments AS comments, 
    o.tmp_cname AS tmp_cname, 
    o.tmp_pname AS tmp_pname, 
    COALESCE(d.number_of_files, 0) AS number_of_files, 
    (CASE o.status WHEN 1 THEN _utf8'completed' 
        WHEN 2 THEN _utf8'hc' 
        WHEN 0 THEN _utf8'not-completed' 
        WHEN 3 THEN _utf8'hc-canceled' 
     END) AS status, 
    o.employee_name AS employee_name, 
    o.status_date AS status_date, 
    o.cancel_reason AS cancel_reason  
FROM 
     tbl_orders_order AS o 
    LEFT JOIN 
     tbl_order_users AS u 
    ON o.user_id = u.user_id 
    LEFT JOIN 
     (SELECT order_id 
       , COUNT(*) AS number_of_files 
     FROM tbl_order_docfiles 
     GROUP BY order_id 
     ) AS d 
    ON d.order_id = o.order_id 

UNION ALL 

SELECT 
    tbl_h.h_date AS sort_col, 
    ... 

FROM tbl_h