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mysql 判斷是否為子集的方法步驟

一、問題

故事起源于一個查詢錯漏率的報表：有兩個查詢結果，分別是報告已經添加的項目和報告應該添加的項目，求報告無遺漏率

何為無遺漏？即，應該添加的項目已經被全部添加

報告無遺漏率也就是無遺漏報告數占報告總數的比率

這里以兩個報告示例（分別是已全部添加和有遺漏的報告）

首先，查出第一個結果——報告應該添加的項目

SELECT 
     r.id AS 報告ID,m.project_id 應添加項目
FROM 
  report r 
  INNER JOIN application a ON r.app_id=a.id
  INNER JOIN application_sample s ON a.id=s.app_id
  RIGHT JOIN application_sample_item si ON s.id=si.sample_id       
  RIGHT JOIN set_project_mapping m ON si.set_id=m.set_id
WHERE r.id IN ('44930','44927')
ORDER BY r.id,m.project_id;

然后，再查出第二個結果——報告已經添加的項目

SELECT r.id AS 報告ID,i.project_id AS 已添加項目 
FROM report r 
RIGHT JOIN report_item i ON r.id=i.report_id
WHERE r.id IN ('44930','44927');

以上就是我們要比較的結果集，不難看出報告44927是無遺漏的，而44930雖然項目數量一致，但實際是多添加了項目758，缺少了項目112，是有遺漏的報告

二、解決方案

從問題看，顯然是一個判斷是否為子集的問題。可以分別遍歷已添加的項目和應該添加的項目，如果應該添加的項目在已添加的項目中都能匹配上，即代表應該添加的項目是已添加的項目子集，也就是無遺漏。

通過循環遍歷比較確實可以解決這個問題，但是SQL中出現笛卡兒積的交叉連接往往意味著開銷巨大，查詢速度慢，那么有沒有辦法避免這一問題呢？

方案一：

借助于函數 FIND_IN_SET和GROUP_CONCAT, 首先認識下兩個函數

FIND_IN_SET(str,strlist)

str: 需要查詢的字符串
strlist: 參數以英文”,”分隔，如 (1,2,6,8,10,22)

FIND_IN_SET 函數返回了需要查詢的字符串在目標字符串的位置

GROUP_CONCAT( [distinct] 要連接的字段 [order by 排序字段 asc/desc ] [separator '分隔符'] )

GROUP_CONCAT()函數可以將多條記錄的同一字段的值，拼接成一條記錄返回。默認以英文‘,'分割。

但是，GROUP_CONCAT()默認長度為1024

所以，如果需要拼接的長度超過1024將會導致截取不全，需要修改長度

SET GLOBAL group_concat_max_len=102400;
SET SESSION group_concat_max_len=102400;

從上述兩個函數介紹中，我們發現FIND_IN_SET和GROUP_CONCAT都以英文‘,'分割（加粗標識）

所以，我們可以用GROUP_CONCAT將已添加項目的項目連接為一個字符串，然后再用FIND_IN_SET逐一查詢應添加項目是否都存在于字符串

1、修改問題中描述中的SQL，用GROUP_CONCAT將已添加項目的項目連接為一個字符串

SELECT r.id,GROUP_CONCAT(i.project_id ORDER BY i.project_id,'') AS 已添加項目列表 
FROM report r 
LEFT JOIN report_item i ON r.id=i.report_id
WHERE r.id IN ('44930','44927')
GROUP BY r.id;

2、用FIND_IN_SET逐一查詢應添加項目是否都存在于字符串

SELECT Q.id,FIND_IN_SET(W.應添加項目列表,Q.已添加項目列表) AS 是否遺漏
   FROM 
   (
   -- 報告已經添加的項目 
      SELECT r.id,GROUP_CONCAT(i.project_id ORDER BY i.project_id,'') AS 已添加項目列表 
      FROM report r 
      LEFT JOIN report_item i ON r.id=i.report_id
      WHERE r.id IN ('44930','44927')
      GROUP BY r.id
   )Q,
   (
   -- 報告應該添加的項目 
      SELECT 
         r.id,s.app_id,m.project_id 應添加項目列表
      FROM 
         report r 
         INNER JOIN application a ON r.app_id=a.id
         INNER JOIN application_sample s ON a.id=s.app_id
         INNER JOIN application_sample_item si ON s.id=si.sample_id       
         INNER JOIN set_project_mapping m ON si.set_id=m.set_id
      WHERE r.id IN ('44930','44927')
      ORDER BY r.id,m.project_id
   )W
   WHERE Q.id=W.id;

3、過濾掉有遺漏的報告

 SELECT Q.id,CASE WHEN FIND_IN_SET(W.應添加項目列表,Q.已添加項目列表)>0 THEN 1 ELSE 0 END AS 是否遺漏
   FROM 
   (
   -- 報告已經添加的項目 
      SELECT r.id,GROUP_CONCAT(i.project_id ORDER BY i.project_id,'') AS 已添加項目列表 
      FROM report r 
      LEFT JOIN report_item i ON r.id=i.report_id
      WHERE r.id IN ('44930','44927')
      GROUP BY r.id
   )Q,
   (
   -- 報告應該添加的項目 
      SELECT 
         r.id,s.app_id,m.project_id 應添加項目列表
      FROM 
         report r 
         INNER JOIN application a ON r.app_id=a.id
         INNER JOIN application_sample s ON a.id=s.app_id
         INNER JOIN application_sample_item si ON s.id=si.sample_id       
         INNER JOIN set_project_mapping m ON si.set_id=m.set_id
      WHERE r.id IN ('44930','44927')
      ORDER BY r.id,m.project_id
   )W
   WHERE Q.id=W.id
   GROUP BY Q.id
   HAVING COUNT(`是否遺漏`)=SUM(`是否遺漏`);

4、我們的最終目標是求無遺漏率

 SELECT COUNT(X.id) 無遺漏報告數,Y.total 報告總數, CONCAT(FORMAT(COUNT(X.id)/Y.total*100,2),'%') AS 項目無遺漏率 FROM 
(
  SELECT Q.id,CASE WHEN FIND_IN_SET(W.應添加項目列表,Q.已添加項目列表)>0 THEN 1 ELSE 0 END AS 是否遺漏
   FROM 
   (
   -- 報告已經添加的項目 
      SELECT r.id,GROUP_CONCAT(i.project_id ORDER BY i.project_id,'') AS 已添加項目列表 
      FROM report r 
      LEFT JOIN report_item i ON r.id=i.report_id
      WHERE r.id IN ('44930','44927')
      GROUP BY r.id
   )Q,
   (
   -- 報告應該添加的項目 
      SELECT 
         r.id,s.app_id,m.project_id 應添加項目列表
       FROM 
         report r 
         INNER JOIN application a ON r.app_id=a.id
         INNER JOIN application_sample s ON a.id=s.app_id
         INNER JOIN application_sample_item si ON s.id=si.sample_id       
         INNER JOIN set_project_mapping m ON si.set_id=m.set_id
       WHERE r.id IN ('44930','44927')
    ORDER BY r.id,m.project_id
   )W
   WHERE Q.id=W.id
   GROUP BY Q.id
   HAVING COUNT(`是否遺漏`)=SUM(`是否遺漏`)
 )X,
 (
    -- 總報告數
    SELECT COUNT(E.nums) AS total FROM
    (
      SELECT COUNT(r.id) AS nums FROM report r 
      WHERE r.id IN ('44930','44927')
      GROUP BY r.id
    )E    
 )Y 
 ;

方案二：

上述方案一雖然避免了逐行遍歷對比，但本質上還是對項目的逐一對比，那么有沒有什么方式可以不用對比呢？

答案當然是有的。我們可以根據統計數量判斷是否完全包含。

1、使用union all 將已添加項目與應添加項目聯表，不去重

 (
 -- 應該添加的項目
SELECT 
  r.id,m.project_id
FROM 
   report r 
INNER JOIN application a ON r.app_id=a.id
INNER JOIN application_sample s ON a.id=s.app_id
INNER JOIN application_sample_item si ON s.id=si.sample_id       
INNER JOIN set_project_mapping m ON si.set_id=m.set_id
WHERE r.id IN ('44930','44927')
ORDER BY r.id,m.project_id
)
UNION ALL
(
 -- 已經添加的項目
select r.id,i.project_id from report r,report_item i 
where r.id = i.report_id and r.id IN ('44930','44927')
group by r.app_id,i.project_id
 )

從結果可以看出，項目同一個報告下有重復的項目，分別代表了應該添加和已經添加的項目

2、根據聯表結果，統計報告重合的項目數量

# 應該添加與已經添加的項目重疊數量
select tt.id,count(*) count from 
(
   select t.id,t.project_id,count(*) from 
   (
      (
        -- 應該添加的項目
        SELECT 
          r.id,m.project_id
        FROM 
          report r 
          INNER JOIN application a ON r.app_id=a.id
          INNER JOIN application_sample s ON a.id=s.app_id
          INNER JOIN application_sample_item si ON s.id=si.sample_id       
          INNER JOIN set_project_mapping m ON si.set_id=m.set_id
        WHERE r.id IN ('44930','44927')
        ORDER BY r.id,m.project_id
      )
      UNION ALL
      (
        -- 已經添加的項目
        select r.id,i.project_id from report r,report_item i 
        where r.id = i.report_id and r.id IN ('44930','44927')
        group by r.app_id,i.project_id
      )
      
   ) t
   GROUP BY t.id,t.project_id
   HAVING count(*) >1 
) tt group by tt.id

3、將第二步的數量與應該添加的數量作比較，如果相等，則代表無遺漏

select bb.id,aa.count 已添加,bb.count 需添加,
    CASE WHEN aa.count/bb.count=1 THEN 1
    ELSE 0
    END AS '是否遺漏' 
from 
(
# 應該添加與已經添加的項目重疊數量
select tt.id,count(*) count from 
(
   select t.id,t.project_id,count(*) from 
   (
      (
        -- 應該添加的項目
        SELECT 
          r.id,m.project_id
        FROM 
          report r 
          INNER JOIN application a ON r.app_id=a.id
          INNER JOIN application_sample s ON a.id=s.app_id
          INNER JOIN application_sample_item si ON s.id=si.sample_id       
          INNER JOIN set_project_mapping m ON si.set_id=m.set_id
        WHERE r.id IN ('44930','44927')
        ORDER BY r.id,m.project_id
      )
      UNION ALL
      (
        -- 已經添加的項目
        select r.id,i.project_id from report r,report_item i 
        where r.id = i.report_id and r.id IN ('44930','44927')
        group by r.app_id,i.project_id
      )
      
   ) t
   GROUP BY t.id,t.project_id
   HAVING count(*) >1 
) tt group by tt.id 
) aa RIGHT JOIN
(
  -- 應該添加的項目數量
  SELECT 
    r.id,s.app_id,COUNT(m.project_id) count
  FROM 
    report r 
    INNER JOIN application a ON r.app_id=a.id
    INNER JOIN application_sample s ON a.id=s.app_id
    INNER JOIN application_sample_item si ON s.id=si.sample_id       
    INNER JOIN set_project_mapping m ON si.set_id=m.set_id
  WHERE r.id IN ('44930','44927')
  GROUP BY r.id
  ORDER BY r.id,m.project_id
) bb ON aa.id = bb.id 
ORDER BY aa.id

4、求出無遺漏率

select 
    SUM(asr.`是否遺漏`) AS 無遺漏數,COUNT(asr.id) AS 總數,CONCAT(FORMAT(SUM(asr.`是否遺漏`)/COUNT(asr.id)*100,5),'%') AS 報告無遺漏率
from 
(
  select bb.id,aa.count 已添加,bb.count 需添加,
      CASE WHEN aa.count/bb.count=1 THEN 1
      ELSE 0
      END AS '是否遺漏' 
  from 
  (
  # 應該添加與已經添加的項目重疊數量
  select tt.id,count(*) count from 
  (
     select t.id,t.project_id,count(*) from 
     (
        (
          -- 應該添加的項目
          SELECT 
            r.id,m.project_id
          FROM 
            report r 
            INNER JOIN application a ON r.app_id=a.id
            INNER JOIN application_sample s ON a.id=s.app_id
            INNER JOIN application_sample_item si ON s.id=si.sample_id       
            INNER JOIN set_project_mapping m ON si.set_id=m.set_id
          WHERE r.id IN ('44930','44927')
          ORDER BY r.id,m.project_id
        )
        UNION ALL
        (
          -- 已經添加的項目
          select r.id,i.project_id from report r,report_item i 
          where r.id = i.report_id and r.id IN ('44930','44927')
          group by r.app_id,i.project_id
        )
        
     ) t
     GROUP BY t.id,t.project_id
     HAVING count(*) >1 
  ) tt group by tt.id 
  ) aa RIGHT JOIN
  (
    -- 應該添加的項目數量
    SELECT 
      r.id,s.app_id,COUNT(m.project_id) count
    FROM 
      report r 
      INNER JOIN application a ON r.app_id=a.id
      INNER JOIN application_sample s ON a.id=s.app_id
      INNER JOIN application_sample_item si ON s.id=si.sample_id       
      INNER JOIN set_project_mapping m ON si.set_id=m.set_id
    WHERE r.id IN ('44930','44927')
    GROUP BY r.id
    ORDER BY r.id,m.project_id
  ) bb ON aa.id = bb.id 
  ORDER BY aa.id
) asr;