Query partitions. in .NET framework

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Query partitions.
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How to Query Partitions
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You can query partitions by using a special function called $PARTITION. The general syntax for this function is as follows:
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[ database_name. ] $PARTITION.partition_function_name(expression)
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The $PARTITION function returns a partition number based on the column values for a particular partition function. The most common ways to use this function are the following:
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Determine the partition number to which a particular value would correspond. Restrict a query to a specific partition.
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The following SELECT query shows how you could use the $PARTITION function to determine the partition number for a given value:
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SELECT $partition.partfunc (2784) as [PartitionNum];
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The following code example shows how to use $PARTITION to restrict a query to a specific partition, in this case, partition number 3:
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SELECT * FROM dbo.CustomerAddress WHERE $partition.partfunc (CustomerAddressID) = 3
6
Creating Partitions
Quick Check
What does the $PARTITION function return The $PARTITION function returns the number of the partition corresponding to the column values for a given partition function.
Quick Check Answer
PRACTICE
Query Partitions
In this practice, you use the $PARTITION function to return the partition number for a given value, the number of rows in each partition that contain data, and all the rows within a specified partition. 1. If necessary, launch SSMS, connect to your instance, open a new query window, and change the context to the partitiontest database. 2. Return the number of rows for each partition by executing the following query:
SELECT $partition.partfunc(id) AS [PartitionNum], count(*) [NumRows] FROM dbo.t1 GROUP BY $partition.partfunc(id) ORDER BY $partition.partfunc(id);
3. Return the partition that the value 4,000 would belong to by executing the following query:
SELECT $partition.partfunc(4000) as [PartitionNum];
4. Return all the rows in partition number 2 by executing the following query:
SELECT * FROM dbo.t1 WHERE $partition.partfunc(id)=2
5. Now, add data to the table and view the results by executing the following batch:
SET NOCOUNT ON DECLARE @i INT, @max INT SELECT @max=MAX(id) + 10 FROM dbo.t1 SET @i= @max WHILE @i<= @max + 3000 - 10 BEGIN INSERT dbo.t1 (id) SELECT @i SET @i=@i+10 END GO --What is the data distribution in the table now SELECT $partition.partfunc(id) AS [PartitionNum], count(*) [NumRows] FROM dbo.t1 GROUP BY $partition.partfunc(id) ORDER BY $partition.partfunc(id) GO
Lesson 4: Querying Partitions
NOTE
Even data distribution
SQL Server does not evenly distribute data between the partitions. The even distribution of data in the initial examples was an accident of how the data was inserted. Data is partitioned on the boundary points only. If a particular partition contains more data than another, it is because more rows match the range defined for the partition. If you want to rebalance the way data is distributed between partitions, you must manually rebalance the distribution by using the operations we will discuss in Lesson 5.
Lesson Summary
You can use the $PARTITION function in a SELECT query to
Determine the partition number to which a particular value belongs. Restrict queries to a specific partition number.
Lesson Review
The following questions are intended to reinforce key information presented in this lesson. The questions are also available on the companion CD if you prefer to review them in electronic form.
NOTE
Answers
Answers to these questions and explanations of why each answer choice is right or wrong are located in the Answers section at the end of the book.
What does the $PARTITION function define A. Boundary points to a partition B. Physical storage for a partition C. A rowset that returns the values in a partition D. The number of the partition containing a specified value
6
Creating Partitions
Lesson 5: Managing Partitions
After you partition a table, index, or indexed view, data modifications cause SQL Server to place rows into the appropriate partition and hence into a specific filegroup on disk. However, partitioning is not a static process. In this lesson, you see how to manage partitions by using three operators: SPLIT, MERGE, and SWITCH.
After this lesson, you will be able to:
Use the SPLIT or MERGE operator to add or remove partitions. Use the SWITCH operator to add and remove rows from a table.
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