mysql - GROUP BY MONTH() 隐藏结果

Question

我正在计算每个月有多少结果。

这是我的查询:

SELECT 
    COUNT(*) as nb,
    CONCAT(MONTH(t.date),0x3a,YEAR(t.date)) as period
FROM table1 t
WHERE t.criteria = 'value'
GROUP BY MONTH(t.date)
ORDER BY YEAR(t.date)

我的结果:

nb  period
---------------
7   6:2009
46  8:2009
2   10:2009
1   11:2009
14  1:2009
9   9:2010
161 7:2010
5   2:2010
88  3:2010
28  4:2010
4   5:2011
2   12:2011

问题是，我确定我在 5:2011 和 12:2011 之间以及其他时间段之间得到了结果自 2009 年以来……:/

这是我的请求还是mysql配置的问题？

非常感谢

Answer 1

您必须同时按年和月进行分组。否则，您 2012 年 4 月的行也会与 2011 年 4 月(和 2010 年 4 月......)的行分组。

SELECT 
    COUNT(*) AS nb,
    CONCAT(MONTH(t.date), ':', YEAR(t.date)) AS period
FROM table1 AS t
WHERE t.criteria = 'value'
GROUP BY YEAR(t.date)
       , MONTH(t.date) ;

---

(您使用 0x3a 而不是 ':' 有什么原因吗？)

---

您还可以使用其他一些 DATE and TIME functions MySQL，因此每行调用的函数更少，查询效率可能更高:

SELECT 
    COUNT(*) AS nb,
    DATE_FORMAT(t.date, '%m:%Y') AS period
FROM table1 AS t
WHERE t.criteria = 'value'
GROUP BY EXTRACT( YEAR_MONTH FROM t.date) ;

---

对于多个查询，在您的数据库中有一个永久日历表(包含所有日期或所有年月)或什至多个日历表是很有用的。示例:

CREATE TABLE CalendarYear
  ( Year SMALLINT UNSIGNED NOT NULL
  , PRIMARY KEY (Year)
  ) ENGINE = InnoDB ;

INSERT INTO CalendarYear
  (Year)
VALUES
  (1900), (1901), ..., (2099) ;

CREATE TABLE CalendarMonth
  ( Month TINYINT UNSIGNED NOT NULL
  , PRIMARY KEY (Month)
  ) ENGINE = InnoDB ;

INSERT INTO CalendarMonth
  (Month)
VALUES
  (1), (2), ..., (12) ;

这些也可以帮助我们制作我们在这里需要的:

CREATE TABLE CalendarYearMonth
  ( Year SMALLINT UNSIGNED NOT NULL
  , Month TINYINT UNSIGNED NOT NULL
  , FirstDay DATE NOT NULL
  , NextMonth_FirstDay DATE NOT NULL
  , PRIMARY KEY (Year, Month)
  ) ENGINE = InnoDB ;

INSERT INTO CalendarYearMonth
  (Year, Month, FirstDay, NextMonth_FirstDay)
SELECT
    y.Year
  , m.Month
  , MAKEDATE(y.Year, 1) + INTERVAL (m.Month-1) MONTH
  , MAKEDATE(y.Year, 1) + INTERVAL (m.Month) MONTH
FROM
    CalendarYear AS y
  CROSS JOIN
    CalendarMonth AS m ;

然后您可以使用日历表来编写更复杂的查询，例如您想要的变体(缺少月份)并且可能更有效。在 SQL-Fiddle 中测试:

SELECT 
    COUNT(t.date) AS nb,
    CONCAT(cal.Month, ':', cal.Year) AS period
FROM
        CalendarYearMonth AS cal
    JOIN
        ( SELECT
              YEAR(MIN(date))  AS min_year
            , MONTH(MIN(date)) AS min_month
            , YEAR(MAX(date))  AS max_year
            , MONTH(MAX(date)) AS max_month
          FROM table1
          WHERE criteria = 'value'
        ) AS mm
      ON  (cal.Year, cal.Month) >= (mm.min_year, mm.min_month)
      AND (cal.Year, cal.Month) <= (mm.max_year, mm.max_month)
    LEFT JOIN
        table1 AS t
      ON  t.criteria = 'value'
      AND t.date >= cal.FirstDay
      AND t.date < cal.NextMonth_FirstDay
GROUP BY 
    cal.Year, cal.Month ;