How expensive is select distinct * query

问题

In sql server 2012, I have got a table with more than 25 million rows with duplicates. The table doesn't have unique index. It only has a non-clustered index. I wanted to eliminate duplicates and so, I m thinking of the below

select distinct * into #temp_table from primary_table
truncate primary_table
select * into primary_table from #temp_table

I wanted to know how expensive is select distinct * query. If my procedure above is very expensive, I wanted to know if there is another alternate way.

回答1:

I don't know how expensive it is, but an alternate way is to create another table with a primary key, insert all the data there and silently reject the duplicates as stated here

http://web.archive.org/web/20180404165346/http://sqlblog.com:80/blogs/paul_white/archive/2013/02/01/a-creative-use-of-ignore-dup-key.aspx

basically, using IGNORE_DUP_KEY

来源：https://stackoverflow.com/questions/22163765/how-expensive-is-select-distinct-query