SQL SERVER

Day 2

Natural Order

• When you do a SELECT FROM the table, the rows will ALWAYS appear in the same order of insertion

• It’s the “natural” chronologically-entered order of the rows

Natural Order

• Table data is stored as a collection of 8-KB (8192-byte) pages.

• 8060 bytes for the data on each page.

• A row of data can not span multiple pages.

Why Optimizer chooses NCI

• a nonclustered index will have less data in its pages than a clustered one

• The size of a nonclustered index will be either equal to or less than the size of a clustered index… it will never be bigger…

Pages and Extents

• The fundamental unit of data storage in SQL Server is the page.

• Size of a page is 8 KB (96-byte header )

• Header store system information about the page:

• Page Number

• Page Type

• Free pace on the page

• Allocation unit ID

Data Page

Extents

• Page type: Data, Index, LOB, ROW_OVERFLOW_DATA etc.

• Extents are the basic unit in which space is managed.

• Extents are a collection of eight physically contiguous pages

ORDER BY CLAUSE

• ORDER BY order_by_expression [ ASC | DESC ] [ ,...n ]

JOINING OF TABLES

• INNER JOIN

• LEFT OUTER JOIN

• RIGHT OUTER JOIN

• FULL OUTER JOIN

• CROSS APPLY

• OUTER APPLY