Oct 21, 2017 · Benefits of a composite primary key. Here is an example of where composite keys represent a rational/beneficial choice as the primary key (PK) (indeed the only rational one as I see it). Think of the classic Databases-101 teaching example of students and courses - the constraints are: one student can take many courses and

How can I move a clustered primary key to a new filegroup? I already have found a possible "algorithm" but it is horribly inefficient: Drop non-clustered indexed (requires them to be resorted and rebuilt) Drop clustered index (requires the whole table to be resorted) Create new primary key constraint (huge sort operation)

Dec 5, 2014 · Is it possible to update a primary key column value with cascading the update among all the foreign keys referencing it ? # EDIT 1: When I run followinq query . select * from sys.foreign_keys where referenced_object_id=OBJECT_ID('myTable') , I see that update_referential_action is set to 0.

Candidate Key is just another key qualified to be a Primary Key. For example, ID is the primary key. But in the same table, if another column for eg. PERSON_ID also can uniquely identify a row, that is called Candidate Key. The 2nd and 3rd normalization rules should hold against all candidate keys also. –

...will fail with a primary key violation in the concurrent scenario (i.e. when inserting the same key that is absent in deleteme from several threads at the same time) with the default transaction isolation level of READ COMMITTED: Error: Violation of PRIMARY KEY constraint 'PK_DeleteMe'. Cannot insert duplicate key in object 'dbo.deleteme'.

Aug 25, 2022 · a primary key constraint on the column that is implemented with the above index. If you create the constraint, the index is created automatically. The constraint seems like an unnecessary adornment at first glance: after all, the index alone already guarantees uniqueness. There are two reasons why a constraint is a good idea, though:

Dec 16, 2014 · If you don't like using primary keys that are auto generated, there is another way. Instead of indexing the userID (which is large and slow to index, because it is a string) you can instead index the hash value of userID.

Nov 11, 2011 · Having a clustered index key with this low selectivity key as the leftmost key, e.g. (state, id), often makes sense because of ranges scans that look for all entries in a particular 'state'. One last note about the possibility of a non-clustered primary key over a heap (i.e. there is no clustered index at all). This may be a valid scenario, the ...

Mar 9, 2021 · Yes, foreign key has to be primary key of parent table. foreign key is not unique it may have duplicate entries. Yes, it may not be unique and may have duplicate entries in child table, but it must be unique and does not have any duplicate entries at the parent table (as it is a primary key). For example consider below tables:

Feb 10, 2015 · As for the primary key choice, it shouldn't even be an issue: your data model, your app logic, should dictate what the primary key is. That being said, my 2c: NVARCHAR(20) is not wide. Is a perfectly acceptable clustered key size, even for a large table.