The following Microsoft SQL Server T-SQL scripts demonstrate large DELETEs.

-- SQL DELETE simple syntax - Create table for testing with SELECT INTO

USE tempdb;

SELECT * INTO Product FROM AdventureWorks2008.Production.Product

-- (504 row(s) affected)

DELETE Product WHERE ListPrice = 0 or Color is NULL

-- (259 row(s) affected)

Instead of DELETE, SELECT INTO what you keep:

-- Backup database
use DatabaseName;
sp_rename TableX, OldTableX;
go
select * into TableX from OldTableX
where (specify criteria for inclusion - what you want to keep)
go
-- create indexes/constraints on TableX
-- Backup database
-- drop table OldTableX -- for example 2 weeks later
go

Alternative to [SELECT INTO new table] is to delete in small batches. Demo follows.

-- SQL DELETE large number of rows from table in batches

USE tempdb;

SELECT ProductID=CONVERT(int,ProductID), ProductName=Name,

       ProductNumber, ListPrice, Color

INTO ProductHuge

FROM AdventureWorks2008.Production.Product

GO

INSERT ProductHuge SELECT * FROM ProductHuge  -- Increase table rows for testing

GO 10

SELECT COUNT(*)FROM ProductHuge

GO

-- 516096

DECLARE @BatchSize int = 10000

-- DELETE loop with 1 sec delay

-- Other processes can use the table during the DELETE

WHILE (@@ROWCOUNT > 0)

BEGIN

  WAITFOR DELAY '00:00:01'

  DELETE TOP (@BatchSize) FROM ProductHuge

  WHERE ListPrice = 0

END

GO

SELECT COUNT(*)FROM ProductHuge

GO

-- 311296

DROP TABLE tempdb.dbo.ProductHuge