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What is composite primary key?
A primary key having two or more attributes is called composite key. It is a combination of two or more columns. Therefore, the Primary Key consisting of two or more attribute is called Composite Key.
What columns should be included in a non-clustered index?
Included columns in a non-clustered index can only be the non-key columns. In the included columns the storage only happens on the leaf level of the index, contrary to the key column of an index. The key column of an index is stored at all levels.
Why is a composite index a non clustered index?
It is a composite non-clustered index because we use multiple columns in the index definition. In the above composite index definition, we defined the order key as FirstName, LastName. Suppose you created the index with the order key as LastName, FirstName.
Which is the first index key column defined in the Composite Index?
It is the first index key column defined in the composite index: It still uses the same execution plan with an index seek operator on the composite index SQL Server. It retrieved 6 records compared to 2 records in the previous examples (1&2) but still using the 4 logical reads for the result.
When to use primary key and nonclustered index?
Primary Key should be uniquely identifying column of the table and it should be NOT NULL. A good (most of the time) candidate of the clustered index key also uniquely identifies column and NOT NULL (most of the time). Well, that means it is a good idea to create a Primary Key Clustered so it solve both the problems together.
Why do we use a composite index in SQL Server?
It is a single index because it uses a single column for the clustered index key. As we can have one clustered index on a SQL table, let’s create a non-clustered index on the [FirstName] and [LastName] columns: It is a composite non-clustered index because we use multiple columns in the index definition.