Is there anything like Parallel CURSOR?

I am using CURSORs to do some row-by-row operation.

OPEN CURSOR_T

FETCH NEXT FROM ...

WHILE @@FETCH_STATUS = 0
BEGIN
      ... Block begins

      ... Block Inserts results into a table

      ... Block terminates
END

I was wondering why this cannot be executed in parallel as the row operations are completely isolated and onl开发者_开发技巧y insert some rows into another table and each row has its own ID assigned so there is no obvious possibility of a conflict.

I was wondering if there is a way to parallelize this in pure SQL?

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This is usually achieved through a queue: you select the 'to do' items and drop them into a queue, and at the same time queue readers (processing threads) are dequeuing the 'to do' items and process them one by one. There is a fine art in using tables as queues, the processing is often associated with activation and the enqueue/dequeue cycle is actually contiguous.

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You could split the from statement in multiple parts, and run them in separate connections. For example, for the first connection, process all rows with an even id:

DECLARE cursor_t CURSOR FOR select id from books where id % 2 = 0

And for the second connection, all rows with an odd id:

DECLARE cursor_t CURSOR FOR select id from books where id % 2 = 1

You could also check if it's possible to eliminate the cursor. If you can rewrite the cursor using set-based operations, it will be much faster, and SQL Server can run it in parallel automatically.