What are the differences between this two statements???

Question

1.select * from counter where eboxid = (select acctid from zsyy_ocecs.cm_subs_subscriber where servnumber = ?);
2.select b.* from zsyy_ocecs.CM_SUBS_SUBSCRIBER a,COUNTER b where a.acctid = b.eboxid and a.servnumber = ?;
what are the differences between the 2 sql statements？？
I WILL APPRECIATE FOR YOUR ANSWERS VERY MUCH, BECAUSE I WAS PUZZLED WHEN I SAW THE EXECUTION PLANS.THANKS AGAIN. MR SHI.
the followings are their execute plans:
Command> select * from counter where eboxid = (select acctid from zsyy_ocecs.cm_subs_subscriber where servnumber = ?);
Query Optimizer Plan:
STEP: 1
LEVEL: 2
OPERATION: TblLkTtreeScan
TBLNAME: ZSYY_OCECS.CM_SUBS_SUBSCRIBER
IXNAME: IDX_SERVNUM
INDEXED CONDITION: CM_SUBS_SUBSCRIBER.SERVNUMBER = qmark_1
NOT INDEXED: ROWNUM < 3
STEP: 2
LEVEL: 2
OPERATION: RowLkTtreeScan
TBLNAME: COUNTER
IXNAME: IDX_COUNTER
INDEXED CONDITION:
COUNTER.EBOXID = CM_SUBS_SUBSCRIBER.ACCTID
NOT INDEXED: <NULL>
STEP: 3
LEVEL: 1
OPERATION: NestedLoop
TBLNAME: <NULL>
IXNAME: <NULL>
INDEXED CONDITION: <NULL>
NOT INDEXED: <NULL>
Command> select b.* from zsyy_ocecs.CM_SUBS_SUBSCRIBER a,COUNTER b where a.acctid = b.eboxid and a.servnumber = ?;
Query Optimizer Plan:
STEP: 1
LEVEL: 2
OPERATION: TmpTtreeScan
TBLNAME: ZSYY_OCECS.CM_SUBS_SUBSCRIBER
IXNAME: <NULL>
INDEXED CONDITION: <NULL>
NOT INDEXED: A.SERVNUMBER = qmark_1
STEP: 2
LEVEL: 2
OPERATION: TblLkTtreeScan
TBLNAME: COUNTER
IXNAME: IDX_COUNTER
INDEXED CONDITION: B.EBOXID
= A.ACCTIDNOT INDEXED: <NULL>
STEP: 3
LEVEL: 1
OPERATION: MergeJoin
TBLNAME: <NULL>
IXNAME: <NULL>
INDEXED CONDITION: A.ACCTID = B.EBOXID
NOT INDEXED: <NULL>
Edited by: user9533799 on 2008-9-3 上午1:28

Answer 1

If zsyy_ocecs.cm_subs_subscriber table returns one row for each servnumber, both statements would return the same data. But if there was a servnumber value on two rows, the first statement will throw an error (you a comparing a value with a set of values). You can rewrite the first query to avoid this:
select * from counter where eboxid in (select acctid from zsyy_ocecs.cm_subs_subscriber where servnumber = ?);
Conceptually they are different and the execution plan can't be the same.