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How to merge new table into existing table

Coding and Syntax

How to merge new table into existing table

by  myearwood  Posted    (Edited  )
Over the years, I've seen people ask how to merge a new table into an existing table. This can be for purposes of a data conversion or a business process to synchronize two systems.

This usually involves a long process to scan the new table, seek in the existing table and either add or replace records.

I once had to merge 100,000 records into 1 million. The original code took several hours. I managed to get it down to about 15 minutes. I've refined that technique to just two commands.

Code: 
UPDATE t ;
	SET ;
		t.field1 = s.field1, ;
		t.field2 = s.field2, ;
		t.field3 = s.field3 ;
	FROM ;
		target t ;
		inner join source s ;
                on t.pk = s.pk ;
	WHERE ;
		t.field1 # s.field1 ;
		OR t.field2 # s.field2 ;
		OR t.field3 # s.field3

INSERT INTO ;
	target ;
	(;
		field1,;
		field2,;
		field3) ;
	SELECT ;
		field1,;
		field2,;
		field3 ;
	FROM ;
		source s ;
	WHERE ;
		s.pk NOT IN ;
		(SELECT pk FROM target)
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