Timeline for Can't define a foreign key
Current License: CC BY-SA 4.0
13 events
| when toggle format | what | by | license | comment | |
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| Jun 18, 2018 at 7:29 | comment | added | hamidi | so i prefer not to use the foreign key and do synchronizations manually. | |
| Jun 18, 2018 at 7:08 | comment | added | Lennart - Slava Ukraini | If you really need to use 0 instead of null you need to add a 0 monitor group. Beside you can't use the action defined on the foreign key, you need to update any monitors for the monitor group before you delete it. | |
| Jun 17, 2018 at 23:49 | comment | added | ypercubeᵀᴹ |
" should set to NULL (identical to 0 for me)" 0 is not identical to NULL in SQL.
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| Jun 17, 2018 at 23:34 | history | migrated | from serverfault.com (revisions) | ||
| Jun 5, 2018 at 7:39 | comment | added | hamidi | Besides, I prefer no Id of a row in MonitorGroups table be set to 0. This is what I want. | |
| Jun 5, 2018 at 7:37 | comment | added | hamidi | I thought it was clear enough. I need not to add any row to MonitorGroups table at first and define the foreign key in such a situation. Certainly all GroupId's in Monitors table should set to NULL (identical to 0 for me). If a GroupId then will have to set to a value other than 0, it should be picked from MonitorGroup table's Id. That's if a GroupId has no value, it's ok. But if it has a value other than 0, it should exist in MonitorGroups table. But I couldn't define such a foreign key. | |
| Jun 3, 2018 at 13:18 | comment | added | TheHe | don't know what you're doing. "0" is a valid value with has to be existent on "MonitorGroups"-Table. NULL just says: no foreign key | |
| Jun 2, 2018 at 14:59 | comment | added | hamidi | I added a row in table Groups with Id zero and this resolved the problem. But I need to know how can I avoid this. | |
| Jun 2, 2018 at 14:58 | vote | accept | CommunityBot | ||
| Jun 2, 2018 at 13:03 | comment | added | hamidi | hmm, see, I need no Id of table MonitorGroups be zero or null. I may allow a row in table Monitors have GroupId of zero, but if assigned another value, it should assign from table MonitorGroups. Is it possible? | |
| Jun 2, 2018 at 12:55 | comment | added | TheHe | NULL is not the problem here? | |
| Jun 2, 2018 at 12:31 | comment | added | hamidi | yes, you're right. as i said, i need to validate existence of rows in table Monitors with GroupId NULL. I know that some database managers support nullable foreign keys, but I'm not sure whether MySQL does it too and how it does. | |
| Jun 2, 2018 at 12:27 | history | answered | TheHe | CC BY-SA 4.0 |