我正在尝试为三列计算非空值。但是，尽管具有不同数量的非空值，但是对于三列中的每一列都返回相同的COUNT。我不确定为什么会这样（我是否需要重新设置列数据类型？错误的SQL子句？）。以下是我的尝试和结果。
编辑：用文字替换图像。制作了较短的别名。
SELECT CAST(users.install_ts AS Date) AS inst_date,
COUNT(users.install_ts) AS total_inst,
COUNT(users.firstlogin_ts) AS total_first_logins,
COUNT(users.firstpurchase_ts) AS conv_cust,
SUM(CASE WHEN users.firstpurchase_ts IS NULL THEN 1 ELSE 0 END) AS conv_cust
FROM users
GROUP BY CAST(users.install_ts AS Date)
inst_date total_inst total_first_logins conv_cust conv_cust
---------- ---------- ------------------ --------- ---------
2015-01-01 17191 17191 17191 0
2015-01-02 41038 41038 41038 0
2015-01-03 41176 41176 41176 0
2015-01-04 41072 41072 41072 0
2015-01-05 41115 41115 41115 0
2015-01-06 8417 8417 8417 0
2015-05-16 9991 9991 9991 0
这是users表：
uid device_id install_ts firstlogin_ts firstpurchase_ts
------ ---------- ------------------- ------------------- -------------------
121045 GalaxyS3 2015-01-01 14:00:01 2015-01-01 14:00:01 (null)
121046 GalaxyS1 2015-01-01 14:00:03 2015-01-01 14:00:07 2015-01-02 06:00:07
121047 iPhone3 2015-01-01 14:00:03 2015-01-01 14:00:03 (null)
121048 GalaxyS1 2015-01-01 14:00:04 (null) (null)
121049 iPhone5 2015-01-01 14:00:07 2015-01-01 14:00:08 (null)
121050 iPad4 2015-01-01 14:00:07 2015-01-01 14:00:09 (null)
121051 iPhone4s 2015-01-01 14:00:11 (null) (null)
121052 iPhone4s 2015-01-01 14:00:13 (null) (null)
121053 GalaxyTab3 2015-01-01 14:00:16 (null) (null)
121054 iPhone4 2015-01-01 14:00:19 2015-01-01 14:00:22 (null)
121055 iPad1 2015-01-01 14:00:22 2015-01-01 14:00:26 (null)
121056 iPad2 2015-01-01 14:00:26 2015-01-01 14:00:29 (null)
121057 GalaxyTab2 2015-01-01 14:00:30 2015-01-01 14:00:31 (null)
121058 iPhone5s 2015-01-01 14:00:34 2015-01-01 14:00:38 (null)
121059 GalaxyS5 2015-01-01 14:00:34 (null) (null)
121060 GalaxyS5 2015-01-01 14:00:34 2015-01-01 14:00:38 (null)
121061 GalaxyS5 2015-01-01 14:00:37 (null) (null)
121062 iPhone3 2015-01-01 14:00:39 (null) (null)
表格说明：
DESCRIBE users
Field Type Null Key Default Extra
---------------- ----------- ---- --- ------------------- ---------------------------
uid int(11) YES MUL (null)
device_id varchar(64) YES (null)
install_ts timestamp NO CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP
firstlogin_ts timestamp NO 0000-00-00 00:00:00
firstpurchase_ts timestamp NO 0000-00-00 00:00:00
编辑：一次执行一个会产生相同的结果。所以也许这是一个分组问题。如果是这样，我该如何实现预期的结果呢？
一次一个：
SELECT COUNT(users.firstlogin_ts) AS total_first_logins
FROM users
GROUP BY CAST(users.install_ts AS Date)
total_first_logins
17191
41038
41176
41072
41115
8417
9991
另一栏：
SELECT COUNT(users.install_ts) AS total_inst
FROM users
GROUP BY CAST(users.install_ts AS Date)
total_inst
17191
41038
41176
41072
41115
8417
9991
答案 0 :(得分：1)
我猜你的问题可能存在显示问题。您显示的数据显示(null)，但表格描述表明字段首先不可为空。但是，字段默认为'0000-00-00 00:00:00'，这不是该类型的有效值，但允许（这很奇怪）。有些API将这些值转换为null，即使它们在数据库中实际上不是NULL。试试这个：
SELECT CAST(users.install_ts AS Date) AS inst_date,
COUNT(1) AS total_inst,
COUNT(NULLIF(users.firstlogin_ts, '0000-00-00 00:00:00')) AS total_first_logins,
COUNT(NULLIF(users.firstpurchase_ts, '0000-00-00 00:00:00')) AS conv_cust
FROM users
GROUP BY CAST(users.install_ts AS Date)
NULLIF会将此类值转换为真值NULL。
答案 1 :(得分：0)
您可以尝试使用https://dba.stackexchange.com/questions/64927/count-null-and-not-null-values-in-a-column
中指定的内容SELECT CAST(users.install_ts AS Date) AS inst_date,
COUNT(!ISNULL(users.install_ts)) AS total_inst,
COUNT(!ISNULL(users.firstlogin_ts)) AS total_first_logins,
COUNT(!ISNULL(users.firstpurchase_ts)) AS conv_cust,
SUM(!ISNULL(users.firstpurchase_ts)) AS conv_cust
FROM users
GROUP BY CAST(users.install_ts AS Date)