如何提高復雜的MySQL選擇查詢的性能？

Question

我正在使用項目管理工具，並且在通過管理端生成報告時，從數據庫中加載數據的時間非常多> 5分鍾。 我知道有幾點可以幫助我提高性能，但是現在我需要在SELECT查詢中獲得幫助

SELECT timesheet_client.organisation as client_name, timesheet_project.title as project_name,
  timesheet_task.name as task, CONCAT(timesheet_user.first_name, ' ', timesheet_user.last_name) as resource_name,
  timesheet_user.bill_factor, timesheet_client.client_type, sum(spent) as spent, sum(delivered_hours) as delivered_hours, 
  sum(billable_hours) as billable_hours, comments, color, lock_color, updated_by, updated_by_date, timesheet_user_psdb.grp_id, 
  timesheet_user_psdb.client_id, timesheet_user_psdb.proj_id, timesheet_user_psdb.task_id, timesheet_user_psdb.uid, 
  timesheet_user_grp.grp_name
FROM timesheet_user_psdb,timesheet_user, timesheet_client, 
  timesheet_project,timesheet_task,timesheet_user_grp
WHERE timesheet_user.username=timesheet_user_psdb.uid and
  timesheet_client.client_id=timesheet_user_psdb.client_id and timesheet_project.proj_id=timesheet_user_psdb.proj_id and
  timesheet_task.task_id = timesheet_user_psdb.task_id and timesheet_user_grp.grp_id=timesheet_user_psdb.grp_id and month =3
  AND year = 2017 and month!='' and timesheet_user_psdb.client_id=326  
GROUP BY timesheet_user_psdb.task_id,timesheet_user_psdb.uid
ORDER BY timesheet_client.client_type desc,timesheet_client.organisation,timesheet_user_psdb.proj_id,
  timesheet_user_psdb.task_id,timesheet_user.uid,timesheet_user_psdb.task_id;

我已經在所有主鍵上使用了索引。

解釋輸出：

對此的幫助將非常可觀。

Answer 1

做EXPLAIN應該會有所啟發。

通過在FROM子句中而不是在WHERE內部進行表聯接，您可能會看到性能提高（ https://dev.mysql.com/doc/refman/5.7/en/join.html ）。 通過執行顯式聯接（例如LEFT OUTER等），您不僅可以提高查詢的可讀性，而且可以在需要的地方使用較便宜的聯接。 這也會影響查詢的執行方式，因為每個子句都以特定順序執行（ MySQL查詢/子句執行順序 ）。

Answer 2

試試看：

SELECT 
    TC.ORGANISATION AS CLIENT_NAME, 
    TP.TITLE AS PROJECT_NAME,
    TT.NAME AS TASK, 
    CONCAT(TU.FIRST_NAME, ' ', TU.LAST_NAME) AS RESOURCE_NAME,
    TU.BILL_FACTOR, 
    TC.CLIENT_TYPE, SUM(SPENT) AS SPENT, -- You should specify which table this comes from
    SUM(DELIVERED_HOURS) AS DELIVERED_HOURS, -- You should specify which table this comes from
    SUM(BILLABLE_HOURS) AS BILLABLE_HOURS, -- You should specify which table this comes from
    COMMENTS, -- You should specify which table this comes from
    COLOR, -- You should specify which table this comes from
    LOCK_COLOR, -- You should specify which table this comes from
    UPDATED_BY, -- You should specify which table this comes from
    UPDATED_BY_DATE, -- You should specify which table this comes from
    TUP.GRP_ID, 
    TUP.CLIENT_ID, 
    TUP.PROJ_ID, 
    TUP.TASK_ID, 
    TUP.UID, 
    TUG.GRP_NAME
FROM    
    TIMESHEET_USER AS TU
        LEFT OUTER JOIN 
    TIMESHEET_USER_PSDB AS TUP
        ON TU.USERNAME = TUP.UID
        LEFT OUTER JOIN
    TIMESHEET_USER_GRP AS TUG
        ON TUP.GRP_ID = TUG.GRP_ID
        LEFT OUTER JOIN     
    TIMESHEET_CLIENT AS TC
        ON TUP.CLIENT_ID = TC.CLIENT_ID
        LEFT OUTER JOIN
    TIMESHEET_PROJECT AS TP
        ON TUP.PROJ_ID = TP.PROJ_ID
        LEFT OUTER JOIN
    TIMESHEET_TASK TT
        ON TUP.TASK_ID = TT.TASK_ID 
WHERE 
    MONTH = 3 AND -- You should specify which table this comes from
    YEAR = 2017 AND -- You should specify which table this comes from
    MONTH != '' AND -- You should specify which table this comes from
    TUP.CLIENT_ID = 326  
GROUP BY 
    TUP.TASK_ID,
    TUP.UID
ORDER BY 
    TC.CLIENT_TYPE DESC,
    TC.ORGANISATION,
    TUP.PROJ_ID,
    TUP.TASK_ID,
    TU.UID,
    TUP.TASK_ID;