Ответы на вопрос:
In MySQL a PRIMARY or UNIQUE KEY creates an index on the columns defined in the constraint. If there are multiple columns a composite index is created.
If its an InnoDB table the PRIMARY KEY also becomes the clustered index for the table.
It doesn't make sense to add additional indexes with the same definitions as a PRIMARY/UNIQUE.
For other RDBMS an index will be required for these constraints. Even if you are allowed to create a constraint without an appropriate index, it will be required to get any reasonable performance.
Популярно: Химия
-
dianka271201.10.2022 11:21
-
zeinebde02.06.2023 08:27
-
tom029183746529.11.2021 16:48
-
Desa1120.11.2022 10:55
-
romanowacristi16.03.2021 19:42
-
dashnv7622.08.2020 17:03
-
repoli43306.09.2022 04:26
-
iodin12.07.2020 15:58
-
ZeBrAiL2TW19.01.2020 13:37
-
ЛенаС12307.07.2021 18:04