How to update one table based on another table ??

Question

Hello Friends:
I am trying to run the following query in oracle but it won't run.
UPDATE BOYS
SET
BOYS.AGE = GIRLS.AGE
FROM GIRLS
WHERE
BOYS.FIRSTNAME = GIRLS.FIRSTNAME AND
BOYS.LASTNAME = GIRLS.LASTNAME;
This query runs fine in sql server but in oracle its saying can't find "SET". PLease tell me what is the correct syntax in oracle to update one table based on another table.
thanks

Answer 1

See if this helps.
If you wrote an SQL statement:
update boys set age = 10;
Every row in the boys table will get updated with an age of 10. But if you wrote:
update boys set age = 10
where firstname = 'Joe';
Then only the rows where the firstname is Joe would be updated with an age of 10.
Now replace the 10 in the above statements with (select g.age from girls g where g.firstname = b.firstname and g.lastname = b.lastname) and replace where firstname = 'Joe' in the second statement with where exists (select null from girls g where g.firstname = b.firstname and g.lastname = b.lastname). The same concepts apply whether 10 is an actual value or a query and whether you have a where clause with the update statement to limit rows being updated.
About the select null question regarding the outer where clause:
Since the query is checking to see if the row in the girls table exists in the boys table what the column is in this select statement doesn't matter, this column isn't being used anywhere. In this case Todd chose to use null. He could have also used a column name from the table or a lot of times you'll see the literal value 1 used here.