在同一表中使用兩個不同值的計數

Question

在以下查詢中，我試圖從表中獲取數據：company,classes_by_company和person。我在名稱爲company_id的所有表中都有一個外鍵。在classes_by_company表中，類可以有class_status，可以是active或inactive。表person及其相應的person_status也是如此。我可以統計班級總人數和總人數，在此查找工作查詢：SQFIDDLE。在下面的查詢中，我試圖合併之前的查詢，但現在也計算總數爲class_status=ACTIVE和person_status=ACTIVE。我收到錯誤Not unique table/alias: 'c'。我怎樣才能算出總人數和活躍班級和人員的總數？ SQLFIDDLE

SELECT a.id, a.company_id, a.status, c.class_status, p.person_status, 
     c.total_count AS classes_per_company, 
     p.total_count AS employees_per_company, 
     c.active_count AS active_classes, 
     p.active_count AS active_instructors 
FROM company a 
LEFT JOIN (SELECT company_id, COUNT(*) as total_count 
      FROM classes_by_company 
      GROUP BY company_id) c 
     ON a.company_id = c.company_id 
LEFT JOIN (SELECT company_id, COUNT(*) as active_count 
      FROM classes_by_company 
      WHERE class_status = 'ACTIVE' 
      GROUP BY company_id) c 
     ON a.company_id = c.company_id 
LEFT JOIN (SELECT company_id, COUNT(*) as total_count 
      FROM person 
      GROUP BY company_id) p 
     ON a.company_id = p.company_id 
LEFT JOIN (SELECT company_id, COUNT(*) as active_count 
      FROM person 
      WHERE person_status = 'ACTIVE' 
      GROUP BY company_id) p 
     ON a.company_id = c.company_id 

表結構：

CREATE TABLE company 
    (
    id int auto_increment primary key, 
    company_id int, 
    status varchar(20) 
    ); 
CREATE TABLE classes_by_company 
(
id int auto_increment primary key, 
company_id int, 
class_name varchar(20), 
class_status varchar(20) 
); 
CREATE TABLE person 
(
id int auto_increment primary key, 
employee_id int, 
company_id int, 
person_name varchar(20), 
person_status varchar(20) 
); 

Answer 1

您所查詢的結構是好的，你只需要爲您加入的每個子查詢提供不同的別名。

您還未能從c和子查詢中返回class_status和person_status。

SELECT a.id, a.company_id, a.status, c.class_status, p.person_status, 
     c.total_count AS classes_per_company, 
     p.total_count AS employees_per_company, 
     ca.active_count AS active_classes, 
     pa.active_count AS active_instructors 
FROM company a 
LEFT JOIN (SELECT company_id, class_status, COUNT(*) as total_count 
      FROM classes_by_company 
      GROUP BY company_id) c 
     ON a.company_id = c.company_id 
LEFT JOIN (SELECT company_id, COUNT(*) as active_count 
      FROM classes_by_company 
      WHERE class_status = 'ACTIVE' 
      GROUP BY company_id) ca 
     ON a.company_id = ca.company_id 
LEFT JOIN (SELECT company_id, person_status, COUNT(*) as total_count 
      FROM person 
      GROUP BY company_id) p 
     ON a.company_id = p.company_id 
LEFT JOIN (SELECT company_id, COUNT(*) as active_count 
      FROM person 
      WHERE person_status = 'ACTIVE' 
      GROUP BY company_id) pa 
     ON a.company_id = pa.company_id 

我更改了活動類別的ca，活動人員的pa。

SQLFIDDLE

您也可以減少一些用在同一個查詢的總行數着活躍的行加入：

SELECT a.id, a.company_id, a.status, c.class_status, p.person_status, 
     c.total_count AS classes_per_company, 
     p.total_count AS employees_per_company, 
     c.active_count AS active_classes, 
     p.active_count AS active_instructors 
FROM company a 
LEFT JOIN (SELECT company_id, class_status, COUNT(*) as total_count, SUM(class_status = 'ACTIVE') as active_count 
      FROM classes_by_company 
      GROUP BY company_id) c 
     ON a.company_id = c.company_id 
LEFT JOIN (SELECT company_id, person_status, COUNT(*) as total_count, SUM(person_status = 'ACTIVE') as active_count 
      FROM person 
      GROUP BY company_id) p 
     ON a.company_id = p.company_id 

SQLFIDDLE

Answer 2

非常小的變化...表別名（或子查詢）不能同

SELECT a.id, a.company_id, a.status, c.class_status, p.person_status, 
    c.total_count AS classes_per_company, 
    p.total_count AS employees_per_company, 
    ca.active_count AS active_classes, 
    pa.active_count AS active_instructors 
FROM company a 
LEFT JOIN (SELECT company_id, COUNT(*) as total_count 
     FROM classes_by_company 
     GROUP BY company_id) c 
    ON a.company_id = c.company_id 
LEFT JOIN (SELECT company_id, COUNT(*) as active_count 
     FROM classes_by_company 
     WHERE class_status = 'ACTIVE' 
     GROUP BY company_id) ca 
    ON a.company_id = c.company_id 
LEFT JOIN (SELECT company_id, COUNT(*) as total_count 
     FROM person 
     GROUP BY company_id) p 
    ON a.company_id = p.company_id 
LEFT JOIN (SELECT company_id, COUNT(*) as active_count 
     FROM person 
     WHERE person_status = 'ACTIVE' 
     GROUP BY company_id) pa 
    ON a.company_id = c.company_id