SQL question

From: Mike Schmitt <mschmitt_at_uchicago.edu>
Date: Thu, 06 May 2004 16:16:01 -0500
Message-Id: <5.2.0.9.2.20040506154456.027afdb0@nsit-imap.uchicago.edu>

I was messing around with SQL, something that I am not very good with, when I ran into something I felt was strange. The SQL from both statements can be seen below, along with their execution plans. I do not quit understand why the 2nd query came back with 3 rows. I know its from user error, but shouldn't Oracle just ignore the test1 table in the second query?

SQL> select a.first_name from test2 a where a.id_number = 2; FIRST_NAME

tom

SQL> select a.first_name from test2 a , test1 c where a.id_number = 2; FIRST_NAME

tom
tom
tom

Execution Plan (1st statement)

0 SELECT STATEMENT Optimizer=CHOOSE 1 0 TABLE ACCESS (FULL) OF 'TEST2' Execution Plan (2nd statement)

0 SELECT STATEMENT Optimizer=CHOOSE 1 0 NESTED LOOPS

    2    1     TABLE ACCESS (FULL) OF 'TEST1'
    3    1     TABLE ACCESS (FULL) OF 'TEST2'







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Received on Thu May 06 2004 - 16:13:21 CDT