How to efficiently delete rows while NOT using Truncate Table in a 500,000+ rows table

Question

Let\'s say we have table Sales with 30 columns and 500,000 rows. I would like to delete 400,000 in the table (those where \"toDelete=\'1\'\").

Answer 1

What you want is batch processing.

While (select Count(*) from sales where toDelete =1) >0
BEGIN
Delete from sales where SalesID in
(select top 1000 salesId from sales where toDelete = 1)
END

Of course you can experiment which is the best value to use for the batch, I've used from 500 - 50000 depending on the table. If you use cascade delete, you will probably need a smaller number as you have those child records to delete.

Answer 2

My own take on this functionality would be as follows. This way there is no repeated code and you can manage your chunk size.

DECLARE @DeleteChunk INT = 10000
DECLARE @rowcount INT = 1

WHILE @rowcount > 0
BEGIN

  DELETE TOP (@DeleteChunk) FROM Sales WITH(ROWLOCK)

  SELECT @rowcount = @@RowCount
END