1. Indexes
CHỈ MỤC DỮ LiỆU

2. Creating Index or not ? Creating index Donot creating index
Speeds up data access
Enforces uniqueness of rows
Donot creating index
Consumes disk space
Incurs overhead
Primary and foreign keys
Frequently searched in ranges
Frequently accessed in sorted order
Seldom referenced in queries
Containing few unique values
Defined with bit, text, or image data types

3. Creating Index Using the CREATE INDEX Statement USE library
CREATE CLUSTERED INDEX cl_lastname ON library..member (lastname)

4. Creating Unique Indexes
USE library
CREATE UNIQUE INDEX title_ident
ON title (title_no) 12
Le Petit Prince
Antoine de Saint-Exupery
~ ~ ~
Duplicate key values are not allowed when a new row is added to the table
title
title_no
author
synopsis 10 11
The Night-Born
Lemon
Walking
Jack London
Motojirou
Henry David Thoreau

5. Creating Composite Indexes
USE library
CREATE UNIQUE INDEX loan_ident
ON loan (isbn, copy_no)
loan
isbn
copy_no
title_no
member_no
342
343 5 10 4 35
3744
5278
3445
out_date
Column 1
Column 2
Composite Key

6. Truy vấn không có index use AdventureWorks SELECT *
INTO Sales.Customer_NoIndex
FROM Sales.Customer
SELECT CustomerID, CustomerType
FROM Sales.Customer_NoIndex
WHERE CustomerID = 11001

7. Truy vấn có index SELECT CustomerID, CustomerType
FROM Sales.Customer_Index
WHERE CustomerID = 11001
SELECT * INTO Sales.Customer_Index FROM Sales.Customer GO CREATE INDEX Idx_CustomerID ON Sales.Customer_Index(CustomerID)

8. SELECT CustomerID, CustomerType FROM Sales
SELECT CustomerID, CustomerType FROM Sales.Customer_NoIndex WHERE CustomerID = FROM Sales.Customer_Index

9. 2 loại indexes Clustered Indexes Non-clustered Indexes
The physical row order of the table and the order of rows in the index are the same
Each table can have only one clustered index
Non-clustered Indexes
Non-clustered indexes are the SQL server default
Existing non-clustered indexes are automatically rebuilt when:
An existing clustered index is dropped
A clustered index is created
The DROP_EXISTING option is used to change which columns define the clustered index