Question

如何在GROUP BY语句中显示所有行？

以下是查询：

SELECT year(feed_date) as date_year, 
       month(feed_date) as date_month, 
       count(*) as nb_item 
FROM table 
WHERE year(feed_date) = '2015' AND
      feed_title LIKE '%word%' AND
      source = '3'
GROUP BY date_year, date_month

这是输出：

-----------------
| 2015 |  7 | 5 |
| 2015 |  9 | 2 |
| 2015 | 10 | 4 |
| 2015 | 11 | 2 |
-----------------

这是所需的输出：

-----------------
| 2015 |  1 | 0 |
| 2015 |  2 | 0 |
| 2015 |  3 | 0 |
| 2015 |  4 | 0 |
| 2015 |  5 | 0 |
| 2015 |  6 | 0 |
| 2015 |  7 | 5 |
| 2015 |  8 | 0 |
| 2015 |  9 | 2 |
| 2015 | 10 | 4 |
| 2015 | 11 | 2 |
| 2015 | 12 | 0 |
-----------------

Answer 1

标签mysqli我可以假设您正在使用PHP。

所以可以这样做：

 $year = '2015';
 $data = [];
 foreach(range(1, 12) AS $month) {
   $data[$month] = [
     'date_year'  => $year,
     'date_month' => $month,
     'nb_item'    => 0
   ];
 }

 $q = "SELECT 
       year(feed_date) as date_year, 
       month(feed_date) as date_month, 
       count(*) as nb_item 
       FROM table 
       WHERE year(feed_date) = '".$year."'
       GROUP BY date_year, date_month";
 $q = mysqli_query($q);
 while($record = mysqli_fetch_assoc($q)) {
   $data[$record['date_month']]['nb_item'] = $record['nb_item'];
 }

 $data = array_values($data);
 print_r($data);

或使用mysql将是一个巨大的查询：

SELECT 
  year(table.feed_date) AS date_year, 
  month(table.feed_date) AS date_month, 
  COALESCE(count(*), 0) as nb_item 
FROM (
  SELECT 1 as month 
  UNION ALL SELECT 2 
  UNION ALL SELECT 3 
  UNION ALL SELECT 4 
  UNION ALL SELECT 5 
  UNION ALL SELECT 6 
  UNION ALL SELECT 7 
  UNION ALL SELECT 8 
  UNION ALL SELECT 9 
  UNION ALL SELECT 10 
  UNION ALL SELECT 11 
  UNION ALL SELECT 12
) months 
LEFT JOIN table ON (months.month = month(table.feed_date))
WHERE year(table.feed_date) = '2015' 
GROUP BY date_year, date_month;

Answer 2

您需要一个包含LEFT JOIN的所有年月组合的表格。您可以通过交叉连接所有年份和月份来动态创建它：

SELECT y.date_year, m.date_month, count(*) as nb_item 
FROM (
    SELECT 1 as date_month UNION ALL
    SELECT 2 UNION ALL
    SELECT 3 UNION ALL
    SELECT 4 UNION ALL
    SELECT 5 UNION ALL
    SELECT 6 UNION ALL
    SELECT 7 UNION ALL
    SELECT 8 UNION ALL
    SELECT 9 UNION ALL
    SELECT 10 UNION ALL
    SELECT 11 UNION ALL
    SELECT 12
) m
CROSS JOIN (
    SELECT 2015 as date_year
) y
LEFT JOIN `table` t 
    ON  year(t.feed_date)  = y.date_year
    AND month(t.feed_date) = m.date_month
    AND t.feed_title LIKE '%word%'
    AND t.source = '3'
GROUP BY y.date_year, m.date_month

如果您有一个包含序列号的帮助表，则可以将查询缩短为：

SELECT y.seq as date_year, m.seq as date_month, count(*) as nb_item 
FROM sequences y
CROSS JOIN sequences m
LEFT JOIN `table` t 
    ON  year(t.feed_date)  = y.date_year
    AND month(t.feed_date) = m.date_month
    AND t.feed_title LIKE '%word%'
    AND t.source = '3'
WHERE y.seq IN (2015)
  AND m.seq <= 12
GROUP BY y.seq, m.seq

Answer 3

您可以使用子查询加入所选数据，该子查询可以从表中获取所有现有年份和月份。

SELECT t1.date_year, t1.date_monthmonth, IFNULL(t2.nb_item, 0) AS nb_item
FROM (SELECT DISTINCT YEAR(feed_date) AS date_year, MONTH(feed_date) AS date_month 
      FROM table) AS t1
LEFT JOIN (
    SELECT year(feed_date) as date_year, 
           month(feed_date) as date_month, 
           count(*) as nb_item 
    FROM table 
    WHERE year(feed_date) = '2015' AND
          feed_title LIKE '%word%' AND
          source = '3'
    GROUP BY date_year, date_month) AS t2
ON t1.date_year = t2.date_year AND t1.date_month = t2.date_month
ORDER BY t1.date_year, t1.date_month

如何显示GROUP BY语句中的所有行？

3 个答案: