Question

I am re-writing a query that was generated by Business Objects and uses “old-fashioned” implicit join syntax. The code joins a table to itself in one part and also has a “global” where clause. For example:

select   a.col1
       , b.col2
from     MYDB.TABLE a, MYDB.TABLE b
where    a.something=b.something_else
     and MYDB.TABLE.source='A'

Above is a made up illustration of the question. The actual query is very long, joining about ten tables.

My question: as written above, does the “extra” where condition apply to both instances of the same table? I think yes, but I’ve never seen code like this before. I’m using Teradata but I think this is a general SQL question.

UPDATE: Perhaps my attempt to narrow the question wasn’t accurate. Here is the complete query I’m trying to modify:

SELECT
  abs_contrct_prof.contrct_nbr_txt,
  gbs_org_LVL1.bus_pln_sgmnt_cd,
  abs_gnrc_lst_of_val_LVL1.wirls_val_1_txt
FROM
  EDWABSUSERVIEWS.abs_contrct  abs_contrct_prof,
  EDWABSUSERVIEWS.gbs_org  gbs_org_LVL1,
  EDWABSUSERVIEWS.abs_gnrc_lst_of_val  abs_gnrc_lst_of_val_LVL1,
  EDWABSUSERVIEWS.abs_contrct,
  EDWABSUSERVIEWS.gbs_sls_actv_blng_org_rltd,
  EDWABSUSERVIEWS.gbs_sls_actv_org_rltd
WHERE
  ( abs_contrct_prof.type_cd = 'PROFILE'  )
  AND  ( EDWABSUSERVIEWS.abs_contrct.type_cd = 'AGREEMENT'  )
  AND  ( abs_contrct_prof.prnt_contrct_id=EDWABSUSERVIEWS.abs_contrct.contrct_id  )
  AND  ( abs_contrct_prof.org_id=EDWABSUSERVIEWS.gbs_sls_actv_org_rltd.org_id  )
  AND  ( EDWABSUSERVIEWS.gbs_sls_actv_org_rltd.gbs_lvl_3_org_id=EDWABSUSERVIEWS.gbs_sls_actv_blng_org_rltd.gbs_lvl_3_org_id  )
  AND  ( EDWABSUSERVIEWS.gbs_sls_actv_blng_org_rltd.gbs_lvl_1_org_id = gbs_org_LVL1.org_id  )
  AND  ( gbs_org_LVL1.bus_pln_sgmnt_cd=abs_gnrc_lst_of_val_LVL1.nm_txt and abs_gnrc_lst_of_val_LVL1.actv_ind = 'Y' and abs_gnrc_lst_of_val_LVL1.type_cd ='ABS_MOBILITY_SEGMENT'  )
  AND  
  abs_contrct_prof.contrct_nbr_txt  IN  @variable('FAN')
  AND  ( EDWABSUSERVIEWS.abs_contrct.sts_cd = 'Active'  )
  AND  ( EDWABSUSERVIEWS.abs_contrct.type_cd='AGREEMENT'  )

Note the table EDWABSUSERVIEWS.abs_contrct is referenced twice in the FROM clause, one time using an alias and once without. And yes, this query works as written, but I want to re-write it to use explict join syntax (as someone commented).

I ran an EXPLAIN on the query and it appears that the “extra” where conditions (for ‘Active’ and ‘AGREEMENT’) are in fact applied to both instances of the table separately.

Answer 1

If your TRANSACTION MODE is TERADATA the optimizer will product join the fully qualified table reference in the WHERE clause against the spool file containing the INNER JOIN results. I have not been able to test this yet with TRANSACTION MODE set to ANSI.

Example

CREATE VOLATILE TABLE Test1
    (
        Col1 SMALLINT NOT NULL,
        col2 VARCHAR(10) NOT NULL
    )
    PRIMARY INDEX (Col1)
    ON COMMIT PRESERVE ROWS;

CREATE VOLATILE TABLE Test2
    (
        Col1 SMALLINT NOT NULL,
        col2 VARCHAR(10) NOT NULL
    )
    PRIMARY INDEX (Col1)
    ON COMMIT PRESERVE ROWS;

SELECT A.Col1
     , B.Col2
     , Test1.Col1
  FROM Test1 A
     , Test2 B
 WHERE A.Col1 = B.Col1
   AND Test1.Col1 = 1;

Explain – Teradata Mode

  1) First, we do an all-AMPs JOIN step from USER.B by way of a RowHash
     match scan with no residual conditions, which is joined to USER.A
     by way of a RowHash match scan with no residual conditions. 
     USER.B and USER.A are joined using a merge join, with a join
     condition of ("USER.A.Col1 = USER.B.Col1").  The result goes into
     Spool 2 (one-amp), which is redistributed by the hash code of (9)
     to all AMPs.  The size of Spool 2 is estimated with low confidence
     to be 1 row (15 bytes).  The estimated time for this step is 0.02
     seconds. 
  2) Next, we do a single-AMP JOIN step from Spool 2 (Last Use) by way
     of an all-rows scan, which is joined to USER.Test1 by way of the
     primary index "USER.Test1.Col1 = 1" with no residual conditions. 
     Spool 2 and USER.Test1 are joined using a product join, with a
     join condition of ("(1=1)").  The result goes into Spool 1
     (all_amps), which is built locally on that AMP.  The size of Spool
     1 is estimated with low confidence to be 1 row (22 bytes).  The
     estimated time for this step is 0.01 seconds. 
  3) Finally, we send out an END TRANSACTION step to all AMPs involved
     in processing the request.
  -> The contents of Spool 1 are sent back to the user as the result of
     statement 1.  The total estimated time is 0.03 seconds. 

UPDATE

INSERT INTO Test1 VALUES (1,'C');
INSERT INTO Test1 VALUES (2,'D');
INSERT INTO Test2 VALUES (1, 'C1');
INSERT INTO Test2 Values (2, 'D2');

Results

Col1  Col2  Test1.Col1
----++----++----------
1     C1    1
2     D2    1

The filter condition was not applied to the tables in the FROM clause.