Hi! Everyone, I have some problems with JOIN and Sub-query; Could you help me, Please?

Dear Sir/Madam
I'm a student who is interested in Oracle Database and
I have some problems with JOIN and Sub-query.
I hope so many of you could help me.
if i use JOIN without sub-query, may it be faster or not?
SELECT field1, field2 FROM tableA INNER JOIN tableB
if i use JOIN with sub-query, may it be faster or not?
SELECT field1,field2,field3 FROM tableA INNER JOIN (SELECT field1,field2 FROM tableB)
Thanks in advance!

Hi,
fac30d8e-74d3-42aa-b643-e30a3780e00f wrote:
Dear Sir/Madam
I'm a student who is interested in Oracle Database and
I have some problems with JOIN and Sub-query.
I hope so many of you could help me.
if i use JOIN without sub-query, may it be faster or not?
SELECT field1, field2 FROM tableA INNER JOIN tableB
if i use JOIN with sub-query, may it be faster or not?
SELECT field1,field2,field3 FROM tableA INNER JOIN (SELECT field1,field2 FROM tableB)
Thanks in advance!
As the others have said, the execution plan will give you a better idea about which is faster.
If you're trying to see how using (or not using) a sub-query affects performance, make the rest of the queries as similar as possible. For example, include field3 in both queries, or ignore field3 in both queries.
In this particular case, I guess the optimizer would do the same thing either way, but that's just a guess. I can't see your execution plans.
In general, simpler code is faster, and better in other ways, too. In this case
tableB
is simpler than
(SELECT field1, field2 FROM tableB)
Why do you want a sub-query in this example?

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