Question

I don’t clearly understand the purpose of using $PARTITION in SQL server? I have read the content from MSDN but don’t still understand.

What benefit can you use it?

Answer 1

Partitioning tables in a database means splitting it into multiple pieces while still treating it like a single table. We are talking here about horizontal partitioning which means that each partition contains all of a columns but only some of the rows. To do this, you have to define a partition function which defines which partition a row belongs to, based on that row’s value in the partitioning column. $PARTITION tells you which partition a row belongs to.

Let’s say we had an integer column that represented the rating of our rows and we expect that users will often ask only for items rated above 4. We could partition based on rating. Our partition function could be:

CREATE PARTITION FUNCTION partitionByRating (int) FOR VALUES (4);

Then, to find out which partition the rows of our table belong to, we could query:

SELECT $partition.partitionByRating(i.Rating) AS [Partition Number],
    rating AS [Rating],
    name AS [Item Name]
FROM dbo.Items AS i

And we might get a result like:

Partition    Rating    Item Name
1            1         Ball
1            4         Scooter
2            5         Blaster

Which means that Ball and Scooter will be stored together, but depending on how you assign partitions to storage, Blaster might be stored somewhere else.