我有两个表t1，t2和以下查询:
SELECT t2.year,
Count(t1.id) AS count
FROM t1,
t2
WHERE t2.t1id = t1.id
AND t2.year IN ( 1995, 1996, 1997, 1998,
1999, 2000 )
GROUP BY t2.year
ORDER BY t1.year
结果是:
+----------+--------+
| year | count |
+----------+--------+
| 1995 | 1 |
| 1998 | 3 |
| 1999 | 3 |
| 2000 | 28 |
+----------+--------+
正如您所看到的，有些年份缺失了。是否可以重写此查询以使其产生结果？
+----------+--------+
| year | count |
+----------+--------+
| 1995 | 1 |
| 1996 | 0 |
| 1997 | 0 |
| 1998 | 3 |
| 1999 | 3 |
| 2000 | 28 |
+----------+--------+
我可以使用 php 并检查缺少哪些行来填补缺少的空白，但这似乎不是很有效。有什么想法吗？
编辑
t1
+-----------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(128) | NO | | NULL | |
+-----------+--------------+------+-----+---------+----------------+
t2
+-----------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| t1id | int(11) | NO | | NULL | |
| year | int(11) | NO | | NULL | |
+-----------+--------------+------+-----+---------+----------------+
例如:
t1
+----------+---------+
| id | name |
+----------+---------+
| 1 | john |
| 2 | bob |
| .. | .. |
+----------+---------+
t2
+----------+---------+---------+
| id | t1id | year |
+----------+---------+---------+
| 100 | 1 | 1995 |
| 101 | 2 | 1998 |
| 103 | 3 | 1998 |
| .. | .. | .. |
+----------+---------+---------+
组合后我最终得到:
+----------+---------+
| id | year |
+----------+---------+
| 100 | 1995 |
| 101 | 1998 |
| 103 | 1998 |
| .. | .. |
+----------+---------+
最佳答案
SELECT t2.year,
IF(Count(t1.id) > 0, Count(t1.id), 0)
FROM t1,
t2
WHERE t2.t1id = t1.id
AND t2.year IN ( 1995, 1996, 1997, 1998,
1999, 2000 )
GROUP BY t2.year
ORDER BY t1.year
关于php - 在 mysql 查询中强制计数为零，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/31546678/