How can we say if Join better than using Sub Queries ??

Question

Hi all,
I am trying to understand the rationale behind "Is _Inner Join_ better than using _Sub Query_ ?" for this scenario ...
I have these tables --
Table1 { *t1_Col_1* (PrimaryKey), t1_Col_2, t1_Col_3, t1_Col_4 }
-- Number of rows = ~4Million , t1_Col_3 has say 60% entries non-zero -----> (Condition 4)
Table2 { *t2_Col_1* (PK), t2_Col_2, t2_Col_3 }
-- Number of rows = ~150Million, t2_Col_2 maps to t1_Col_1 -----> (Condition 1). This means for every distinct value of t1_Col_1 (its PK) we'll have multiple rows in Table2.
Table3 { *t3_Col_1* (PK), t3_Col_2, t3_Col_3 }
-- Number of rows = ~50K, t3_Col_1 maps to t1_Col_2 -----> (Condition 2)
Table4 { *t4_Col_1* (PK), t4_Col_2, t4_Col_3 }
-- Number of rows = ~1K, t4_Col_2 maps to t3_Col_2 -----> (Condition 3)
Now here are the 2 queries: -
Query using direct join --
SELECT t1_Col_1, t2_Col_1, t3_Col_1, t4_Col_2
FROM Table1, Table2, Table3, Table4
WHERE t1_Col_1=t2_Col_2 -- Condition 1
AND t1_Col_2=t3_Col_1 -- Condition 2
AND t3_Col_2=t4_Col_1 -- Condition 3
AND t1_Col_3 != 0
Query using SubQuery --
SELECT t1_Col_1, t2_Col_1, t3_Col_1, t4_Col_2
FROM Table2,
(SELECT t1_Col_1, t3_Col_1, t4_Col_2
FROM Table1,Table3, Table4
WHERE
AND t1_Col_2=t3_Col_1 -- Condition 2
AND t3_Col_2=t4_Col_1 -- Condition 3
AND t1_Col_3!= 0
WHERE t1_Col_1=t2_Col_2 -- Condition 1
Now the golden question is - How can I document with evidence that Type-1 is better than Type-2 or the other way ? I think the 3 things in comparison are: -
- Number of rows accessed (Type-1 better ?)
- Memory/Bytes used (Again Type-1 better ?)
- Cost ( ?? )
(PS - testing on both MySQL, Oracle10g)
Thanks,
A

Answer 1

So, is it right to conclude that Optimizer uses the optimal path and then processes the query resulting in nearly the same query execution time ?If the optimizer transforms two queries so that they end up the same, then they will run in the same time. Of course, sometimes it cannot do so because of the the way the data is defined (nulls are often a factor; constraints can help it) or the way the query is written, and sometimes it misses a possible optimization due to inaccurate statistics or other information not available to it, or limitations of the optimizer itself.
Is this the right place to ask for MySQL optimization ?Probably not.