Question

我正在创建一个查询，该查询从两个表中提取某些用户的视图数。
当找不到结果（即SUM为零）时，我正在努力寻找一种显示“ n / a”的方法。

这是两个表：

个人资料：
-profile_id
-profile_name

观看次数：
-profile_id
-日期
-观看次数

这是查询：

SELECT 
    p.profile_name,
    Jan,
    Feb,
    Mar,
    Apr,
    May,
    Jun,
    Jul,
    Aug,
    Sep,
    Oct,
    Nov,
    December as 'Dec' 
FROM profiles p

LEFT JOIN (SELECT 
    profile_id,
    SUM(IF(MONTH(date) = 1,views,0)) As 'Jan',
    SUM(IF(MONTH(date) = 2,views,0)) As 'Feb',
    SUM(IF(MONTH(date) = 3,views,0)) As 'Mar',
    SUM(IF(MONTH(date) = 4,views,0)) As 'Apr',
    SUM(IF(MONTH(date) = 5,views,0)) As 'May',
    SUM(IF(MONTH(date) = 6,views,0)) As 'Jun',
    SUM(IF(MONTH(date) = 7,views,0)) As 'Jul',
    SUM(IF(MONTH(date) = 8,views,0)) As 'Aug',
    SUM(IF(MONTH(date) = 9,views,0)) As 'Sep',
    SUM(IF(MONTH(date) = 10,views,0)) As 'Oct',
    SUM(IF(MONTH(date) = 11,views,0)) As 'Nov',
    SUM(IF(MONTH(date) = 12,views,0)) As 'December'
    FROM views 
WHERE YEAR(date) = '2016'
GROUP BY profile_id) v
ON (p.profile_id = v.profile_id)
ORDER BY p.profile_name

我一直在寻找一种方法，在找不到结果时显示“ n / a”。

这是我现在得到的结果：

+---------------------+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+
| Profile        2016 | Jan    | Feb    | Mar    | Apr    | May    | Jun    | Jul    | Aug    | Sep    | Oct    | Nov    | Dec    |
+---------------------+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+
| Anna Wintour        | 0      | 0      | 0      | 0      | 649693 | 575615 | 658556 | 603785 | 588790 | 0      | 586767 | 639005 |
| Karl Lagerfeld      | 635900 | 626585 | 612628 | 586811 | 656580 | 536151 | 598911 | 646069 | 650960 | 594483 | 591757 | 683251 |
| Pierre Alexis Dumas | 629109 | 579499 | 647326 | 585578 | 597296 | 618063 | 603452 | 617052 | 586233 | 588641 | 604276 | 623885 |
| Sandra Choi         | 592426 | 590954 | 648027 | 564362 | 633135 | 612299 | 606808 | 629006 | 631480 | 680511 | 565733 | 573343 |
| Tom Ford            | 552798 | 603373 | 550430 | 709178 | 662036 | 608399 | 708395 | 610961 | 629205 | 628796 | 616628 | 712198 |
+---------------------+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+

Answer 1

如果您要在一个月内未找到任何视图时显示N/A，请将每个SUM更改为以下形式：

COALESCE(SUM(CASE WHEN MONTH(date) = 1 THEN views END), 'N/A') As 'Jan',

这样，如果一个月内没有观看次数，则SUM的结果将为NULL（因为CASE表达式的值将为NULL ），然后COALESCE会将其转换为N/A。

Demo on dbfiddle

由于mysql SUM，添加字符串而不是结果0

1 个答案: