Timeline for Why does a UNIQUE constraint allow only one NULL in SQL Server?
Current License: CC BY-SA 3.0
5 events
| when toggle format | what | by | license | comment | |
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| Jul 24, 2023 at 19:46 | comment | added | Kenneth Fisher | @liquidki I'll admit the useful part is entirely my own opinion. If the index is on col1, col2, col3 someone tries to insert a second copy of (1, null, 2) I would rather then unique index disallow that rather than allow 1000's of copies just because one of the columns has a null value. | |
| Jun 8, 2023 at 16:15 | comment | added | liquidki | @KennethFisher You noted that they did this to make it more useful. I'm curious about that. Do you know why they considered it more useful than the ANSI standard? | |
| Oct 17, 2014 at 19:27 | comment | added | Kenneth Fisher | @ypercube True. That's why I said it was just the implementation and doesn't really fit in with the definition of NULL. I hadn't thought about the filtered unique index (although I've used it for other things.) | |
| Oct 17, 2014 at 18:39 | comment | added | ypercubeᵀᴹ | This (SQL-Server's) technicality also doesn't fit with the SQL standard. There is a 7-year old Connect item about this issue. | |
| Oct 17, 2014 at 18:34 | history | answered | Kenneth Fisher | CC BY-SA 3.0 |