Need a help on Update statement

Question

Hi All,
I Need a help in updating a table column. PFB my requirement.
Table1
ItemID OrgId       Date
1       82     12/sep/2012   
2       82     25/oct/2012
3       82     17/Nov/2012
4     82     22/Jan/2013
5     82     26/sep/2012
Table2
Itemid     orgid       Date1
1      82     23/sep/2012      
2      82     25/Dec/2012
3      82     17/Sep/2012
4      82     22/Feb/2013
5      82     26/Oct/2012
Table3
Itemid     orgid       Date3
1      82     10/sep/2012      
7      82     30/Dec/2012
3      82     12/Sep/2012
10      82     27/Feb/2013
5      82     29/Oct/2012
I Need to Update Date column of Table1 With Date3 of table3
If
Item and org combination is present in table3 and date column of table1 is less than Date3 of table3
Else
I need to Update with date2 of table2.Can we acheive this in a single update statement, can any one help me on this.
Thanks and regards,
Rakesh
Edited by: Venkat Rakesh on Sep 27, 2012 11:04 PM

Answer 1

You can probably also use MERGE:
--DROP TABLE table1;
--DROP TABLE table2;
--DROP TABLE table3;
ALTER SESSION SET nls_language = 'AMERICAN';
CREATE TABLE table1
   itemid    CHAR (1),
   orgid     CHAR (2),
   thedate   DATE
INSERT INTO table1   SELECT '1', '82', TO_DATE ('10/sep/2011', 'dd/mon/yyyy') FROM DUAL;
INSERT INTO table1   SELECT '2', '82', TO_DATE ('10/oct/2011', 'dd/mon/yyyy') FROM DUAL;
INSERT INTO table1   SELECT '3', '82', TO_DATE ('10/nov/2011', 'dd/mon/yyyy') FROM DUAL;
INSERT INTO table1   SELECT '4', '82', TO_DATE ('10/jan/2011', 'dd/mon/yyyy') FROM DUAL;
INSERT INTO table1   SELECT '5', '82', TO_DATE ('10/sep/2011', 'dd/mon/yyyy') FROM DUAL;-- won't be updated
CREATE TABLE table2
   itemid    CHAR (1),
   orgid     CHAR (2),
   thedate   DATE
INSERT INTO table2   SELECT '1', '82', TO_DATE ('01/sep/2012', 'dd/mon/yyyy') FROM DUAL;
INSERT INTO table2   SELECT '2', '82', TO_DATE ('01/dec/2012', 'dd/mon/yyyy') FROM DUAL;
INSERT INTO table2   SELECT '3', '82', TO_DATE ('01/sep/2012', 'dd/mon/yyyy') FROM DUAL;
INSERT INTO table2   SELECT '4', '82', TO_DATE ('01/feb/2012', 'dd/mon/yyyy') FROM DUAL;
CREATE TABLE table3
   itemid    CHAR (1),
   orgid     CHAR (2),
   thedate   DATE
INSERT INTO table3   SELECT '2', '82', TO_DATE ('30/dec/2009', 'dd/mon/yyyy') FROM DUAL; -- date less than table1, so picks from table2
INSERT INTO table3   SELECT '4', '82', TO_DATE ('30/mar/2013', 'dd/mon/yyyy') FROM DUAL; -- larger than table1 , so pick this date
-- table1 original data
SELECT * FROM table1;
-- merge new data
MERGE INTO table1
     USING (SELECT NVL (t1.itemid, t2.itemid) itemid,
                   NVL (t1.orgid, t2.orgid) orgid,
                   t2.thedate prefdate ,
                   t1.thedate nextdate
              FROM    table2 t1
                   FULL OUTER JOIN
                      table3 t2
                   ON t1.itemid = t2.itemid AND t1.orgid = t2.orgid) dat
        ON (dat.itemid = table1.itemid AND dat.orgid = table1.orgid)
WHEN MATCHED
THEN
   UPDATE SET table1.thedate = (case when prefdate > table1.thedate then prefdate else nextdate end) ;
--table1 updated data
SELECT * FROM table1;OUTPUT:
Session altered.
Table created.
1 row created.
1 row created.
1 row created.
1 row created.
1 row created.
Table created.
1 row created.
1 row created.
1 row created.
1 row created.
Table created.
1 row created.
1 row created.
ITEMID ORGID THEDATE  
1      82    10.09.2011
2      82    10.10.2011
3      82    10.11.2011
4      82    10.01.2011
5      82    10.09.2011
5 rows selected.
4 rows merged.
ITEMID ORGID THEDATE  
1      82    01.09.2012
2      82    01.12.2012
3      82    01.09.2012
4      82    30.03.2013
5      82    10.09.2011
5 rows selected.