[英]In a mysql UNION can I exclude rows from the left part in the right part
我有一张表,用于存储个人或组的记录。
|id|entity_id|person_id|group_id|
|1 |000000001|999999999|NULL |
|2 |000000001|NULL |88888888|
|3 |000000002|999999999|NULL |
|4 |000000003|NULL |88888888|
如何获取 person_id 999999999 和 group_id 88888888 的所有记录,但后者仅在我没有 person_id 999999999 的 entity_id 000000001 的记录时
所以我的结果应该是
|id|entity_id|person_id|group_id|
|1 |000000001|999999999|NULL |
|3 |000000002|999999999|NULL |
|4 |000000003|NULL |88888888|
我希望这在一个查询中是可能的,但是 UNION, EXCEPT 似乎并不能解决问题。
我正在尝试类似的东西
SELECT *
from myTable m1
WHERE NOT IS NULL person_id
UNION ALL
SELECT *
from myTable m2
WHERE NOT IS NULL group_id
EXCEPT (SELECT entity_id FROM m1)
但显然 mysql 不支持 EXCEPT
使用NOT EXISTS
:
SELECT t1.*
FROM tablename t1
WHERE t1.person_id = '999999999'
OR (
t1.group_id = '88888888'
AND NOT EXISTS (SELECT 1 FROM tablename t2 WHERE t2.entity_id = t1.entity_id AND t2.person_id = '999999999')
)
请参阅演示。
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