tailieunhanh - Hướng dẫn học Microsoft SQL Server 2008 part 149

Một giá trị biên giới chỉ có thể tồn tại trong một phân vùng. Những dãy được xác định là trái hoặc phải. Nếu một hàng có giá trị cột phân vùng đó là giống như một giá trị ranh giới, sau đó SQL Server cần biết trong đó phân vùng để đặt hàng. Còn lại các phạm vi có nghĩa là dữ liệu bằng ranh giới được bao gồm trong các phân vùng bên trái của ranh giới. | Part IX Performance Tuning and Optimization FIGURE 68-3 The partition function is used by the partition scheme to place the data in separate filegroups. Boundaries defined by the Partition Function Partition Locations defined by the Partition Scheme only specify the boundary values between ranges they don t define the upper or lower values for the whole table. A boundary value can only exist in one partition. The ranges are defined as left or right. If a row has a partition column value that is the same as a boundary value then SQL Server needs to know in which partition to put the row. Left ranges mean that data equal to the boundary is included in the partition to the left of the boundary. A boundary of 12 31 2004 would create two partitions. The lower partition would include all data up to and including 12 31 2004 and the right partition would include any data greater than 12 31 2004 . Right ranges mean that data equal to the boundary goes into the partition on the right of the boundary value. To separate at the new year starting 2008 a right range would set the boundary at 1 1 2008 . Any values less than the boundary go into the left or lower boundary. Any data with a date equal to or later than the boundary goes into the next partition. These two functions use left and right ranges to create the same result CREATE PARTITION FUNCTION pfyears DateTime AS RANGE LEFT FOR VALUES 12 31 2001 12 31 2002 12 31 2003 12 31 2004 or CREATE PARTITION FUNCTION pfYearsRT DateTime AS RANGE RIGHT FOR VALUES 1 1 2002 1 1 2003 1 1 2004 1 1 2008 These functions both create four defined boundaries and thus five partitions. 1442 Partitioning 68 l 7 Z n SQL Server 2008 s table partitions are declarative meaning the table is segmented by data values. A hash partition segments the data randomly. SQL Server does not have hash par- titioning. You can create a hash function on a computed column but your client application needs to understand this computation to allow