MySQL 2表联合
我请求你理解,因为我英语说得不好 有四张桌子MySQL 2表联合,mysql,Mysql,我请求你理解,因为我英语说得不好 有四张桌子 sensor (PK: sensor) sensor | service 1 | 1 2 | 2 equipment (PK: id, FK: sensor) id | equip | sensor | 1 | 8 | 1 | 2 | 8 | 1 | 3 | 8 | 2 | 4 | 7 | 2 | A (PK: AUTO INCREM
sensor (PK: sensor)
sensor | service
1 | 1
2 | 2
equipment (PK: id, FK: sensor)
id | equip | sensor |
1 | 8 | 1 |
2 | 8 | 1 |
3 | 8 | 2 |
4 | 7 | 2 |
A (PK: AUTO INCREMENT, UNIQUE: id, time, FK: id)
id | time | temperature
1 | 1027 | 30
1 | 1028 | 30
1 | 1029 | NULL
1 | 1030 | 60
1 | 1101 | 999
B (PK: AUTO INCREMENT, UNIQUE: id, time, FK: id)
id | time | temperature
2 | 1027 | 40
2 | 1029 | 50
2 | 1030 | NULL
2 | 1031 | 59
我想要以下结果
time | A_temperature | B_temperature
1027 | 30 | 40
1028 | 30 | NULL
1029 | NULL | 50
1030 | 60 | NULL
1031 | NULL | 59
因此,我提出了以下问题:
SELECT DISTINCT COALESCE(A.time, B.time) time, A.temperature AS A_temperature, B.temperature AS B_temperature
FROM equipment AS equip
JOIN sensor sen
ON sen.sensor = equip.sensor
AND sen.service = 1
JOIN A
ON A.id = equip.id
AND (A.time>= '1027' AND A.time<= '1031')
LEFT JOIN B
ON B.id = equip.id
AND (B.time>= '1027' AND B.time<= '1031')
AND B.time= A.time
WHERE equip.equip = 8
UNION
SELECT DISTINCT COALESCE(B.time, A.time) time, A.temperature AS A_temperature, B.temperature AS B_temperature
FROM equipment AS equip
JOIN sensor sen
ON sen.sensor = equip.sensor
AND sen.service = 1
LEFT JOIN B
ON B.id = equip.id
AND (B.time>= '1027' AND B.time<= '1031')
AND B.time= A.time
JOIN A
ON A.id = equip.id
AND (A.time>= '1027' AND A.time<= '1031')
WHERE equip.equip = 8
ORDER BY time ASC;
执行上述查询后,
A.time
和B.time
被分离,并输出结果。我想同时合并这些。如果时间为null
,我们希望将其设置为非null时间。我认为您可以通过创建一个子查询来简化前面问题的答案,该子查询只选择表a
和B
中所有不同的时间值。然后,您可以分别将A
和B
表加入其中,并按时间值分组,使用MAX
聚集温度,因为这些值将有效或NULL
,而MAX
将忽略:
SELECT t.time, MAX(A.temperature) AS A_temperature, MAX(B.temperature) AS B_temperature
FROM equipment e
JOIN sensor s ON s.sensor = e.sensor AND s.service = 1
JOIN (SELECT time FROM A UNION SELECT time FROM B) t
LEFT JOIN A on A.id = e.id AND A.time = t.time
LEFT JOIN B on B.id = e.id AND B.time = t.time
WHERE t.time BETWEEN 1027 AND 1031
GROUP BY t.time
ORDER BY t.time
输出:
time A_temperature B_temperature
1027 30 40
1028 30
1029 50
1030 60
1031 59
非常感谢您!我挣扎了很多,不用担心。很高兴我能帮忙。
time A_temperature B_temperature
1027 30 40
1028 30
1029 50
1030 60
1031 59