当 CASE 不存在时，SQL 计数返回 0

Question

我有两个表 Log 和 Player。其中 Log 存储带有 playerId 和日期的每个游戏日志。并且 Player 表的 Players 信息为 Age 和 Gender ..etc。我正在编写一个 SQL 存储过程，它需要两个日期，并将按两个日期之间的年龄范围和性别计算 LogId 和组。但是当我运行 SQL 过程时，当该期间没有玩家存在时，它不会显示所有 Age_Range/Gender 条目。我正在尝试获取所有 Age_Range/Gender 条目及其实际计数或计数 = 0，如果他们不不存在。 我什至尝试过改变

count(L.LogId) as Count, 

到

count(IFNULL(L.LogId, 0)) as Count,

我的SQL程序是：

CREATE PROCEDURE `SHOW_AGE_RANGE` (IN date1 CHAR(10), IN date2 CHAR(10))
 BEGIN
 SELECT
  count(L.LogId) as Count,
  CASE
     WHEN P.age BETWEEN 13 AND 18 THEN '13-18'
     WHEN P.age BETWEEN 19 AND 25 THEN '19-25'
     WHEN P.age BETWEEN 26 AND 39 THEN '26-39'
     WHEN P.age BETWEEN 40 AND 59 THEN '40-59'
     WHEN P.age > 59 THEN '60+' 
 END as Age_Range,
 CASE
    WHEN P.gender  = 0 then 'Female'
    WHEN P.gender  = 1 then 'Male'
 END  as Gender    
 FROM Log L
 LEFT JOIN Player P ON L.playerId = P.playerId 

 WHERE CAST(L.createdDate AS DATE) BETWEEN CAST(date1 AS DATE) AND CAST(date2 AS DATE)  
 GROUP BY Age_Range, Gender;    
END

SQL 过程的输出：

Count  Age_Range  Gender 
----------------------------------
'1'    '13-18'    'Male'
'1'    '19-25'    'Female'
'3'    '26-39'    'Female'
'2'    '40-59'    'Male'
'1'    '60+'      'Female'

预期输出

Count  Age_Range  Gender 
----------------------------------
'0'    '13-18'    'Female'
'1'    '13-18'    'Male'
'1'    '19-25'    'Female'
'0'    '19-25'    'Male'
'3'    '26-39'    'Female'
'0'    '26-39'    'Male'
'0'    '40-59'    'Female'
'2'    '40-59'    'Male'
'1'    '60+'      'Female'
'0'    '60+'      'Male'

Answer 1

您需要从您的年龄范围和性别开始。真的，您正在查询这些，而玩家数据只是您添加到它们的东西。由于您的表中还没有年龄范围（您可能应该考虑添加它），因此您需要为这些表创建一个虚拟表作为子查询。

SELECT
    COUNT(L.playerId) AS cnt,
    AG.age_range,
    G.gender
FROM
(
    SELECT 13 AS min_age, 18 AS max_age, '13-18' AS age_range
    UNION ALL
    SELECT 19 AS min_age, 25 AS max_age, '19-' AS age_range
    UNION ALL
    SELECT 26 AS min_age, 39 AS max_age, '26-39' AS age_range
    UNION ALL
    SELECT 40 AS min_age, 59 AS max_age, '40-59' AS age_range
    UNION ALL
    SELECT 60 AS min_age, 999 AS max_age, '60+' AS age_range
) AS AG
CROSS JOIN
(
    SELECT 0 AS gender_value, 'Female' AS gender
    UNION ALL
    SELECT 1 AS gender_value, 'Male' AS gender
) AS G
LEFT JOIN Player P ON
    P.age BETWEEN AG.min_age AND AG.max_age AND
    P.gender = G.gender_value
LEFT OUTER JOIN Log L ON
    L.playerId = P.playerId AND
    CAST(L.createdDate AS DATE) BETWEEN CAST(date1 AS DATE) AND CAST(date2 AS DATE)
GROUP BY
    AG.age_range, G.gender

Answer 2

看起来您想要Log 表的外部联接。交换Player 和Log 表，并将createdDate 列上的谓词重新定位到ON 子句。

像这样：

  FROM Player P
  LEFT 
  JOIN Log L
    ON L.playerId = P.playerId 
   AND CAST(L.createdDate AS DATE) BETWEEN CAST(date1 AS DATE) AND CAST(date2 AS DATE)
 GROUP BY Age_Range, Gender;