View source for Using Common Table Expressions in Oracle to update tables

=== Example: Merge / Fix PrimaryKeyColumnSequences from the MaxSysIndex and MaxSysKeys tables ===

<syntaxhighlight lang=SQL>

/*
** Merge / Fix PrimaryKeyColumnSequences from the MaxSysIndex and MaxSysKeys tables
*/
MERGE INTO maxsyscolscfg d
   USING
   (
	select indexname, m.tbname, m.name, colname, m.primarykeycolseq, colseq from (
	with indexes as
		(select name as indexname, tbname, colname, colseq
			 from maxsyskeys k
			inner join maxsysindexes i on i.name = k.ixname and uniquerule = 'U'
			and name like '%NDX1'
		)
		select * from indexes
		) i
	join maxsyscolscfg m on m.tbname = i.tbname and m.name = i.colname
	where (primarykeycolseq != colseq or (primarykeycolseq is null and colseq is not null))
	) s
   ON (d.tbname = s.tbname and d.name = s.name)
   WHEN MATCHED THEN UPDATE SET d.primarykeycolseq = s.colseq
   WHEN NOT MATCHED THEN insert (d.tbname) values (s.tbname) --where (d.primarykeycolseq != s.primarykeycolseq)
;

MERGE INTO maxsyscolumns d
   USING
   (
	select indexname, m.tbname, m.name, colname, m.primarykeycolseq, colseq from (
	with indexes as
		(select name as indexname, tbname, colname, colseq
			 from maxsyskeys k
			inner join maxsysindexes i on i.name = k.ixname and uniquerule = 'U'
			and name like '%NDX1'
		)
		select * from indexes
		) i
	join maxsyscolumns m on m.tbname = i.tbname and m.name = i.colname
	where (primarykeycolseq != colseq or (primarykeycolseq is null and colseq is not null))
	) s
   ON (d.tbname = s.tbname and d.name = s.name)
   WHEN MATCHED THEN UPDATE SET d.primarykeycolseq = s.colseq
   WHEN NOT MATCHED THEN insert (d.tbname) values (s.tbname) --where (d.primarykeycolseq != s.primarykeycolseq)
;

commit
;
</syntaxhighlight>