Quick insert or update of records from a second table

There are some cases when you need to update an existing record in a table from another table or insert a new record if one doesn't exist. Here is a quick way to do either procedure. 

                
/*  
TABLE_MAIN 

code_id  period  empl_id  amount 
----------------- ----------- --------- 
105       200108    100      500 
100       200108    100      300 
100       200109    100      250 
105       200109    100      350 
100       200110    200       0 
150       200110    200       0 

TABLE_NEW 

code_id     period      amount 
------  -----------  ---------- 
100         200110      500 
105         200110      900 
150         200110      200 
100         200111      375 
105         200111      750 
150         200111      900 

--update existing in TABLE_MAIN records with new amount 
        from the TABLE_NEW 
*/ 
UPDATE  TABLE_MAIN 
SET amount= n.amount 
 FROM TABLE_MAIN t LEFT OUTER JOIN TABLE_NEW n 
        ON t.code_id = n.code_id AND t.period = n.period 
WHERE n.code_id IS NOT NULL 

-- 'Insert new records into TABLE_MAIN 

INSERT INTO  TABLE_MAIN(code_id, period, amount) 
SELECT  n.code_id , n.period, n.amount 
FROM  TABLE_NEW n LEFT OUTER JOIN TABLE_MAIN t 
        ON t.code_id = n.code_id AND t.period = n.period 
WHERE t.code_id IS  NULL 

go 

/*

Final results:

code_id period empl_id   amount 
------------ ----------- --------- 
105      200108   100         500 
100

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 200108   100         300 
100      200109   100         250 
105      200109   100         350 
100      200110   200         500 
150      200110   200         200 
100      200111   NULL       375 
105      200110   NULL       900 
105      200111   NULL       750 
150      200111   NULL       900 
*/

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This was first published in January 2002

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