SQL COUNT(*) return 0 IFNULL with WHERE 子句和 GROUP_BY on same table

Question

即使计数为 null，结果也应该 return 包含日期的一行。

SELECT DATE_FORMAT(created_date, '%Y-%m') AS date, COUNT(*) AS total
FROM mytable
WHERE created_date BETWEEN :startDate AND :endDate 
AND condition = :condition
GROUP BY DATE_FORMAT(created_date, '%Y-%m')
ORDER BY created_date ASC

我看到我应该使用 LEFT JOIN 和 IFNULL，但我尝试了但没有很好的结果。

想要的结果：

array(1) {
  [0]=> {
    ["date"]=>
    string(7) "2016-01"
    ["total"]=>
    string(1) "0"
  }
  [1]=> {
    ["date"]=>
    string(7) "2016-02"
    ["total"]=>
    string(4) "9492"
  }
  [2]=> {
    ["date"]=>
    string(7) "2016-03"
    ["total"]=>
    string(1) "0"
  }
}

PS ：我正在使用 MySQL

Answer 1

LEFT JOIN 是正确的，但是 table 你所做的 Left join。您需要 calendar table 和 List dates

当没有找到特定 date 的记录时，您不必使用 IFNULL，然后 Count 聚合将 return 0

SELECT Date_format(c.dates, '%Y-%m') AS date,
       Count(m.created_date)         AS total
FROM   Calendar_table c
       LEFT JOIN mytable m
              ON c.dates = Cast(m.created_date AS DATE)
WHERE  created_date BETWEEN :startDate AND :endDate
       AND condition = :condition
GROUP  BY Date_format(c.dates, '%Y-%m')
ORDER  BY c.dates ASC

为了创造calendartable他是一篇文章：Calendar Tables: An Invaluable Database Tool

SQL COUNT(*) return 0 IFNULL with WHERE 子句和 GROUP_BY on same table

SQL COUNT(*) return 0 IFNULL with WHERE clauses and GROUP_BY on same table

mysql

sql

count

sql-order-by

ifnull