Why don't this query fails??

Question

Hi All,
A little brainstorming ....
I am providing the sql here..
Connected to Oracle Database 11g Enterprise Edition Release 11.2.0.1.0
Connected as dss
SQL>
SQL>   UPDATE dw_mmg_cat_us
  2    SET    dw_eftv_to = TRUNC(sysdate)
  3    WHERE  (mcv_mc_mc_id,mcv_mcv_id,mmg_mmg_id) IN
  4           (SELECT mcv_mc_mc_id,mcv_mcv_id,mmg_mmg_id
  5           FROM   dw_mmg_cat_us
  6           WHERE  dw_eftv_to is null
  7           AND    mcv_mc_mc_id = 'DUMP_NO'
  8           MINUS
  9           SELECT mcv_mc_mc_id,mcv_mcv_id,mmg_mmg_id
10           FROM   merc_mmg_catus
11          WHERE  mcv_mc_mc_id = 'DUMP_NO');
0 rows updated
SQL>
SQL> SELECT mcv_mc_mc_id,mcv_mcv_id,mmg_mmg_id
  2  FROM   dw_mmg_cat_us
  3  WHERE  dw_eftv_to is null
  4  AND    mcv_mc_mc_id = 'DUMP_NO'
  5  MINUS
  6  SELECT mcv_mc_mc_id,mcv_mcv_id,mmg_mmg_id
  7  FROM   merc_mmg_catus
  8  WHERE  mcv_mc_mc_id = 'DUMP_NO'
  9  /
SELECT mcv_mc_mc_id,mcv_mcv_id,mmg_mmg_id
FROM   dw_mmg_cat_us
WHERE  dw_eftv_to is null
AND    mcv_mc_mc_id = 'DUMP_NO'
MINUS
SELECT mcv_mc_mc_id,mcv_mcv_id,mmg_mmg_id
FROM   merc_mmg_catus
WHERE  mcv_mc_mc_id = 'DUMP_NO'
ORA-00904: "MCV_MC_MC_ID": invalid identifier
SQL> desc dw_mmg_cat_us
Name         Type         Nullable Default Comments                                                        
MCV_MC_MC_ID VARCHAR2(10)                  Merchandise category                                            
MCV_MCV_ID   VARCHAR2(10)                  The value for the category                                      
MMG_MMGL_ID  NUMBER(3)                     The unique identifier of the MMGL                               
MMG_MMG_ID   VARCHAR2(10)                  The identifier of the MMG, unique within the significant level  
DW_EFTV_FROM DATE                          Date the relationship was effective from No direct mapping from 
DW_EFTV_TO   DATE         Y                Date the relationship is effective to No direct mapping from exi
SQL> select * from merc_mmg_catus where rownum < 5;
MMG_ART_MMG_ID MC_MC_ID   MCV_MCV_ID
            12 CLASSTYPE  O
            13 CLASSTYPE  O
            14 CLASSTYPE  O
            15 CLASSTYPE  O
SQL>
SQL> SELECT mcv_mc_mc_id,mcv_mcv_id,mmg_mmg_id
  2  FROM   merc_mmg_catus
  3  WHERE  mcv_mc_mc_id = 'DUMP_NO'
  4  /
SELECT mcv_mc_mc_id,mcv_mcv_id,mmg_mmg_id
FROM   merc_mmg_catus
WHERE  mcv_mc_mc_id = 'DUMP_NO'
ORA-00904: "MCV_MC_MC_ID": invalid identifierHere merc_mmg_catus is the synonym it is not a table? But this object does not have mcv_mc_mc_id,mmg_mmg_id
these two field so why the above update statement is not failing. if i separately select this query it throws error as above.. then why this is not throwing in the update statement.
Thanks,
Sid

Answer 1

>
SQL>   UPDATE dw_mmg_cat_us
  2    SET    dw_eftv_to = TRUNC(sysdate)
  3    WHERE  (mcv_mc_mc_id,mcv_mcv_id,mmg_mmg_id) IN
  4           (SELECT mcv_mc_mc_id,mcv_mcv_id,mmg_mmg_id
  5           FROM   dw_mmg_cat_us
  6           WHERE  dw_eftv_to is null
  7           AND    mcv_mc_mc_id = 'DUMP_NO'
  8           MINUS
  9           SELECT mcv_mc_mc_id,mcv_mcv_id,mmg_mmg_id
10           FROM   merc_mmg_catus
11          WHERE  mcv_mc_mc_id = 'DUMP_NO');When resolving names that have no prefix, Oracle will have to try and figure out what you mean.
The column names in line 9 have no prefix, so Oracle will try to figure it out.
It will check if the columns come from the table(s) in the from clause (line 10), as that is not the case it can find the column names in the table in line 1.
So I think it has resolved the names to be like this:
SQL>   UPDATE dw_mmg_cat_us d3
  2    SET    d3.dw_eftv_to = TRUNC(sysdate)
  3    WHERE  (d3.mcv_mc_mc_id,d3.mcv_mcv_id,d3.mmg_mmg_id) IN
  4           (SELECT d1.mcv_mc_mc_id,d1.mcv_mcv_id,d1.mmg_mmg_id
  5           FROM   dw_mmg_cat_us d1
  6           WHERE  d1.dw_eftv_to is null
  7           AND    d1.mcv_mc_mc_id = 'DUMP_NO'
  8           MINUS
  9           SELECT d3.mcv_mc_mc_id,d3.mcv_mcv_id,d3.mmg_mmg_id
10           FROM   merc_mmg_catus d2
11          WHERE  d2.mcv_mc_mc_id = 'DUMP_NO');Which doesn't make much sense, but is syntactically valid.
If you make a habit of prefixing column names, you would probably have written something like:
SQL>   UPDATE dw_mmg_cat_us d3
  2    SET    d3.dw_eftv_to = TRUNC(sysdate)
  3    WHERE  (d3.mcv_mc_mc_id,d3.mcv_mcv_id,d3.mmg_mmg_id) IN
  4           (SELECT d1.mcv_mc_mc_id,d1.mcv_mcv_id,d1.mmg_mmg_id
  5           FROM   dw_mmg_cat_us d1
  6           WHERE  d1.dw_eftv_to is null
  7           AND    d1.mcv_mc_mc_id = 'DUMP_NO'
  8           MINUS
  9           SELECT d2.mcv_mc_mc_id,d2.mcv_mcv_id,d2.mmg_mmg_id
10           FROM   merc_mmg_catus d2
11          WHERE  d2.mcv_mc_mc_id = 'DUMP_NO');Which would have failed because Oracle could see that d2 does not have those columns.