MySQL 查询不返回所有记录

Question

我的数据库中有几个表，我使用左外连接来连接这些表并执行查询。问题是，并不是所有匹配的记录都被返回，第一个总是由于某种原因从结果中被跳过。

这是 SQL Fiddle 的链接,

架构 + 测试数据:

mysql> select * from main;
+----------+------------+----------------+---------------+-------------+-------------+----------------+----------------+-----------------+------------+------------+----------------+-----------------+---------------+--------------------------+--------------+
| username | date       | water_quantity | water_chilled | smoked_what | smoke_count | sleep_duration | study_duration | screen_duration | loud_level | heat_level | humidity_level | stress_physical | stress_mental | stress_notes             | menstruation |
+----------+------------+----------------+---------------+-------------+-------------+----------------+----------------+-----------------+------------+------------+----------------+-----------------+---------------+--------------------------+--------------+
| test123  | 2012-09-16 |              1 | no            | cigarettes  |          20 |            480 |              0 |             420 |          2 |          7 |              7 |               6 |             4 | Roamed a lot on the bike | no           |
| test123  | 2012-09-13 |              2 | no            | cigarettes  |          12 |            300 |              0 |               0 |          1 |          1 |              1 |               6 |             3 | met friends              | no           |
+----------+------------+----------------+---------------+-------------+-------------+----------------+----------------+-----------------+------------+------------+----------------+-----------------+---------------+--------------------------+--------------+
2 rows in set (0.00 sec)

mysql> select * from food;
+----------+------------+--------------+
| username | date       | food         |
+----------+------------+--------------+
| test123  | 2012-09-16 | rice         |
| test123  | 2012-09-16 | pizza        |
| test123  | 2012-09-16 | french fries |
| test123  | 2012-09-16 | burger       |
| test123  | 2012-09-13 | naan         |
| test123  | 2012-09-13 | fried rice   |
| test123  | 2012-09-13 | lemon juice  |
+----------+------------+--------------+
7 rows in set (0.00 sec)

mysql> select * from alcohol;
+----------+------------+--------------+------------------+
| username | date       | alcohol_type | alcohol_quantity |
+----------+------------+--------------+------------------+
| test123  | 2012-09-16 | beer         |                0 |
| test123  | 2012-09-16 | beer_ale     |                0 |
| test123  | 2012-09-16 | absinthe     |                0 |
| test123  | 2012-09-13 | rum          |                0 |
| test123  | 2012-09-13 | tequila      |                0 |
+----------+------------+--------------+------------------+
5 rows in set (0.00 sec)

mysql> select * from headache;
+----------+------------+-----------+----------+---------------------+
| username | date       | intensity | duration | notes               |
+----------+------------+-----------+----------+---------------------+
| test123  | 2012-09-16 |         6 |       12 | something something |
+----------+------------+-----------+----------+---------------------+
1 row in set (0.00 sec)

mysql> select * from headache_areas;
+----------+------------+-----------------+
| username | date       | area            |
+----------+------------+-----------------+
| test123  | 2012-09-16 | left_temple     |
| test123  | 2012-09-16 | right_temple    |
| test123  | 2012-09-16 | behind_left_ear |
+----------+------------+-----------------+
3 rows in set (0.00 sec)

mysql> select * from headache_symptoms;
+----------+------------+-----------+
| username | date       | symptoms  |
+----------+------------+-----------+
| test123  | 2012-09-16 | aura      |
| test123  | 2012-09-16 | vertigo   |
| test123  | 2012-09-16 | dizziness |
+----------+------------+-----------+
3 rows in set (0.00 sec)

mysql> select * from alcohol;
+----------+------------+--------------+------------------+
| username | date       | alcohol_type | alcohol_quantity |
+----------+------------+--------------+------------------+
| test123  | 2012-09-16 | beer         |                0 |
| test123  | 2012-09-16 | beer_ale     |                0 |
| test123  | 2012-09-16 | absinthe     |                0 |
| test123  | 2012-09-13 | rum          |                0 |
| test123  | 2012-09-13 | tequila      |                0 |
+----------+------------+--------------+------------------+
5 rows in set (0.00 sec)

mysql> select * from drugs;
+----------+------------+----------+
| username | date       | drug     |
+----------+------------+----------+
| test     | 2012-08-21 | crocin   |
| test     | 2012-08-21 | azithral |
| test     | 2012-08-21 | crocin   |
| test     | 2012-08-21 | azithral |
| test     | 2012-08-21 | crocin   |
| test     | 2012-08-21 | azithral |
| test123  | 2012-09-13 | ching    |
| test123  | 2012-09-13 | chong    |
| test123  | 2012-09-13 | blah1    |
| test123  | 2012-09-13 | blurg2   |
+----------+------------+----------+
10 rows in set (0.00 sec)

我尝试的查询结果:

mysql> SELECT m.*,
    ->                 GROUP_CONCAT(DISTINCT f.food SEPARATOR ',') AS food, 
    ->                 GROUP_CONCAT(DISTINCT a.alcohol_type SEPARATOR ',') AS alcohol,
    ->                 a.alcohol_quantity,
    ->                 GROUP_CONCAT(DISTINCT d.drug SEPARATOR ',') AS drug,
    ->                 h.intensity AS headache_intensity,
    ->                 h.duration AS headache_duration,
    ->                 GROUP_CONCAT(DISTINCT ha.area) AS headache_areas,
    ->                 GROUP_CONCAT(DISTINCT hs.symptoms) AS headache_symptoms,
    ->                 h.notes AS headache_notes
    ->             FROM main AS m 
    ->                 LEFT OUTER JOIN food AS f ON f.username = m.username AND f.date = m.date 
    ->                 LEFT OUTER JOIN headache AS h ON h.username = m.username AND h.date = m.date
    ->                 LEFT OUTER JOIN headache_symptoms AS hs ON hs.username = m.username AND hs.date = m.date
    ->                 LEFT OUTER JOIN headache_areas AS ha ON ha.username = m.username AND ha.date = m.date
    ->                 LEFT OUTER JOIN drugs AS d ON d.username = m.username AND d.date = m.date
    ->                 LEFT OUTER JOIN alcohol AS a ON a.username = m.username AND a.date = m.date
    ->            ;
+----------+------------+----------------+---------------+-------------+-------------+----------------+----------------+-----------------+------------+------------+----------------+-----------------+---------------+--------------------------+--------------+------------------------------------------------------------+------------------------------------+------------------+--------------------------+--------------------+-------------------+------------------------------------------+------------------------+---------------------+
| username | date       | water_quantity | water_chilled | smoked_what | smoke_count | sleep_duration | study_duration | screen_duration | loud_level | heat_level | humidity_level | stress_physical | stress_mental | stress_notes             | menstruation | food                                                       | alcohol                            | alcohol_quantity | drug                     | headache_intensity | headache_duration | headache_areas                           | headache_symptoms      | headache_notes      |
+----------+------------+----------------+---------------+-------------+-------------+----------------+----------------+-----------------+------------+------------+----------------+-----------------+---------------+--------------------------+--------------+------------------------------------------------------------+------------------------------------+------------------+--------------------------+--------------------+-------------------+------------------------------------------+------------------------+---------------------+
| test123  | 2012-09-16 |              1 | no            | cigarettes  |          20 |            480 |              0 |             420 |          2 |          7 |              7 |               6 |             4 | Roamed a lot on the bike | no           | rice,pizza,french fries,burger,naan,fried rice,lemon juice | beer,beer_ale,absinthe,rum,tequila |                0 | ching,chong,blah1,blurg2 |                  6 |                12 | left_temple,right_temple,behind_left_ear | aura,vertigo,dizziness | something something |
+----------+------------+----------------+---------------+-------------+-------------+----------------+----------------+-----------------+------------+------------+----------------+-----------------+---------------+--------------------------+--------------+------------------------------------------------------------+------------------------------------+------------------+--------------------------+--------------------+-------------------+------------------------------------------+------------------------+---------------------+
1 row in set (0.00 sec)

它没有显示表中的其他记录。有人可以帮我解决这个问题吗？提前致谢。

Answer 1

它准确地输出您“要求它”执行的操作(通过使用 group concat):

USERNAME    |...| FOOD                                                       | ALCOHOL  ...
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
test123     |...| rice,pizza,french fries,burger,naan,fried rice,lemon juice |  beer,beer_ale,absinthe,rum,tequila  ...

当您使用 group concat 时，它会将 grouped 列的所有值连接到一个输出字段中。

更新:
我想我知道你想要实现的目标，因为它在表 main 的两个记录中都是相同的用户名，它将显示为一列，解决这个问题你需要找到第一个字段这两条记录不相同 - 即 date。所以你所要做的就是将 GROUP BY m.username, date 添加到 end of your query .