In SQL Server, the CREATE PARTITION FUNCTION statement is used to define a partition function, which maps the set of values to a set of partitions. This is an essential step in implementing partitioned tables or indexes, as it determines how data is divided among the partitions based on the values specified.
Here’s the syntax for creating a partition function:
CREATE PARTITION FUNCTION partition_function_name (numeric_type)
AS RANGE {LEFT | RIGHT} FOR VALUES (value1, value2, ...);
Breakdown of the Syntax
- partition_function_name: Specify the name of the partition function you are creating.
- numeric_type: This specifies the data type of the values used to define the partitions (e.g., INT, BIGINT, DATETIME, etc.).
- RANGE: Indicates the range boundary. This can be LEFT or RIGHT, which determines where the boundary values for the partitions fall.
- RANGE LEFT: The boundary value is included in the partition to its left.
- RANGE RIGHT: The boundary value is included in the partition to its right.
- FOR VALUES: This clause specifies the list of values that define the boundaries for each partition.
Example
Here’s a simple example of creating a partition function for an integer type, partitioning on a range of values:
CREATE PARTITION FUNCTION pfRange (INT)
AS RANGE LEFT FOR VALUES (100, 200, 300);
Explanation of the Example
1. Function Name: The name of the partition function is pfRange.
2. Type: It is defined for the INT data type.
3. Range Behavior: It utilizes RANGE LEFT, meaning that each range will include the boundary value:
- Partition 1 will include all values less than or equal to 100.
- Partition 2 will include values greater than 100 and less than or equal to 200.
- Partition 3 will include values greater than 200 and less than or equal to 300.
- Partition 4 will contain values greater than 300.
Additional Steps
After creating a partition function, you generally also create a partition scheme using the CREATE PARTITION SCHEME statement to define how these partitions are mapped to filegroups. Afterward, you can create a partitioned table or index that uses this scheme and function.
Make sure that the values specified in FOR VALUES are sorted in ascending order, and there are no duplicate values to avoid errors during creation.