Delete large amount of data in sql server

Question

Suppose that I have a table with 10000000 record. What is difference between this two solution?

1. delete data like :

   DELETE FROM MyTable
            
   
   
           

Answer 1

The first has clearly better performance.

When you specify DELETE [MyTable] it will simply erase everything without doing checks for ID. The second one will waste time and disk operation to locate a respective record each time before deleting it.

It also gets worse because every time a record disappears from the middle of the table, the engine may want to condense data on disk, thus wasting time and work again.

Maybe a better idea would be to delete data based on clustered index columns in descending order. Then the table will basically be truncated from the end at every delete operation.