sql - UNIQUE argument for INDEX creation - what's for? -


Why is the unique argument in the index creation statement?

As I have understood, the non-cluster index should be unique to a bookmark, an indicator in a row, which should be unique to differentiate between non-unique rows;
-Clustered index should be exclusive? Is that right?

So, do I think that any unique index can not be on the cluster table?

  • "A compiled index should be unique on one view" [1]

Because "the bottom, or the leaf, the level of the package index is the table's actual data Rows "[1], do I correctly believe that the same effect as the UNIUE on the package index can be achieved by a unique obstacle on a table [possibly all or some part] [2]? >

Then, what would bring unique logic for the index?
Definitions of basic concepts, except illusions [3]

UPDATE:
It is again the same threat - explained some already explained several times already Without that it can be understood that all explanations are based on the changing game.
Please see my subquisan [4] which is actually the re-wording of this same question.

Update 2:
The problem is in ambiguous, inappropriate use of words in definitions or inappropriate contexts. If the index is defined as the (identity and) identification / pointing structure for the actual data, then the non-unique or null index does not make any sense. Bye

Cited:
[1] Create Indexes (Transact-SQL)

[2]
Create Tabs (Transact- SQL)

[3]
Unique index or unique key?

[4]
What is the index and the non-clustered index is exclusive

Unique index clause is actually only a chime of syntax in SQL Server and some other DBMSs. In standard SQL, the lack of specificity is implemented through the use of the primary key and unique syntax syntax, not through the index (there is no index in standard SQL).

The system uses internally to limit the SQL server specificity is called a unique index whenever you create a primary key or unique obligation, a unique index is automatically created for you. Because of the well-known reasons for SQL Server Development Team, they advertise unique keywords as part of unique index syntax Decided to do, even though constraint syntax same thing.

In the interest of supporting clarity and standards, I advise you to avoid making unique lists clearly wherever possible. Instead use the primary key or the UNQIUE barrier syntax.


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