OraQA » XML http://oraqa.com Oracle Question and Answer Thu, 09 Dec 2010 04:07:45 +0000 http://wordpress.org/?v=2.8.4 en hourly 1 How to select from an alternative table when the table in the From Clause doesn’t exist in the database http://oraqa.com/2010/12/08/how-to-select-from-an-alternative-table-when-the-table-in-the-from-clause-doesnt-exist-in-the-database/ http://oraqa.com/2010/12/08/how-to-select-from-an-alternative-table-when-the-table-in-the-from-clause-doesnt-exist-in-the-database/#comments Thu, 09 Dec 2010 04:07:45 +0000 Frank Zhou http://oraqa.com/?p=630 The following is an interesting problem posted on an internet website:

select a.id, b.str
from TARGET_TAB a, lookup_tab b WHERE a.id = b.id

If “TARGET_TAB” Table doesn’t exist in the database, then the alternative table “ALTERNATIVE_TAB” should be used instead.

select a.id, b.str
from ALTERNATIVE_TAB a, lookup_tab b WHERE a.id = b.id

Requirement : Solve this problem by using a single sql query.

create table TARGET_TAB as select level as id from dual connect by level <4;
create table ALTERNATIVE_TAB as select level as id from dual connect by level <6;
create table lookup_tab as select level as id, chr(64+level) str from dual connect by level <6;

————————————————————-SQL Solution———————————————–

WITH XML AS
(SELECT dbms_xmlgen.getxml('SELECT id FROM '||table_name) xml_clob
 FROM user_tables
 WHERE table_name IN
    (SELECT 'TARGET_TAB' FROM dual
      UNION ALL
      SELECT 'ALTERNATIVE_TAB' FROM dual
      WHERE NOT EXISTS (SELECT NULL FROM user_tables WHERE table_name = 'TARGET_TAB')
     )
 ),
 DATA AS
( SELECT ID
  FROM   XML,  XMLTable('ROWSET/ROW'
                         PASSING XMLTYPE(XML.xml_clob)
                         COLUMNS
                         ID NUMBER PATH 'ID')
 )
 SELECT a.ID, str
 FROM DATA a, lookup_tab b
 WHERE a.ID = b.id;

        ID S
---------- -
         1 A
         2 B
         3 C     

drop table target_tab;

Run the same SQL again.

        ID S
---------- -
         1 A
         2 B
         3 C
         4 D
         5 E
]]> http://oraqa.com/2010/12/08/how-to-select-from-an-alternative-table-when-the-table-in-the-from-clause-doesnt-exist-in-the-database/feed/ 0 How to Generate XML Data from the Database http://oraqa.com/2006/04/27/how-to-generate-xml-data-from-the-database/ http://oraqa.com/2006/04/27/how-to-generate-xml-data-from-the-database/#comments Thu, 27 Apr 2006 20:01:16 +0000 Eddie Awad http://oraqa.com/2006/04/27/how-to-generate-xml-data-from-the-database/ You can generate XML from the database using:

  • Standard SQL/XML Functions:
    • XMLELEMENT
    • XMLATTRIBUTES
    • XMLFOREST
    • XMLCONCAT
    • XMLAGG
    • XMLPI
    • XMLCOMMENT
    • XMLROOT
    • XMLSERIALIZE
    • XMLPARSE
  • Oracle Database SQL Functions:
    • XMLSEQUENCE
    • XMLCOLATTVAL
    • XMLCDATA
    • SYS_XMLGEN
    • SYS_XMLAGG
  • DBMS_XMLGEN
  • XSQL Pages Publishing Framework
  • XML SQL Utility (XSU)
  • DBURIType

Some of the options above may not be available in versions of the Oracle database earlier than 10g Release 2 (10.2).

For more details on each of the above options check out:

Related links:

If you have any additional XML resources, please add them in the comments below.

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