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原创 IT综合 作者:atgc 时间:2007-07-13 10:51:11 0 删除 编辑

and we said...

There are at least 2 ways to perform this sort of co-related update correctly.  I'll show 
my preferred method (update a join) and then another method that'll work if you cannot 
put a unique constraint on LOOKUP(keyname) (which is needed for the join update).


Here are the test tables:

scott@ORA734.WORLD> create table name
  2  ( keyname int,
  3    columnName varchar2(25)
  4  )
  5  /
Table created.

scott@ORA734.WORLD> create table lookup
  2  ( keyname int PRIMARY KEY,
  3    value varchar2(25),
  4    otherColumn int
  5  )
  6  /
Table created.

scott@ORA734.WORLD> insert into name values ( 100, 'Original Data' );
1 row created.

scott@ORA734.WORLD> insert into name values ( 200, 'Original Data' );
1 row created.

scott@ORA734.WORLD> insert into lookup values ( 100, 'New Data', 1 );
1 row created.

scott@ORA734.WORLD> commit;
Commit complete.


here is the "other_value" parameter you are using in the above update you 
attempted...

scott@ORA734.WORLD> variable other_value number
scott@ORA734.WORLD> exec :other_value := 1
PL/SQL procedure successfully completed.

scott@ORA734.WORLD> select * from name;

   KEYNAME COLUMNNAME
---------- -------------------------
       100 Original Data
       200 Original Data


Here we update a join.  We can only modify the columns in one of the tables and the 
other tables we are *NOT* modifying must be "key preserved" -- that is, we must be able 
to verify that at most one record will be returned when we join NAME to this other table. 
 In order to do that, keyname in LOOKUP must either be a primary key or have a unique 
constraint applied to it...

scott@ORA734.WORLD> update
  2    ( select columnName, value
  3        from name, lookup
  4       where name.keyname = lookup.keyname
  5         and lookup.otherColumn = :other_value )
  6     set columnName = value
  7  /

1 row updated.

scott@ORA734.WORLD> select * from name;

   KEYNAME COLUMNNAME
---------- -------------------------
       100 New Data
       200 Original Data

See, the other data is untouched and only the rows we wanted are updated..

scott@ORA734.WORLD> rollback;
Rollback complete.

scott@ORA734.WORLD> select * from name;

   KEYNAME COLUMNNAME
---------- -------------------------
       100 Original Data
       200 Original Data


Now, this way will work with no constraints on anything -- you do not need the primary 
key/unique constraint on lookup (but you better be sure the subquery returns 0 or 1 
records!).

It is very much like your update, just has a where clause so that only rows that we find 
matches for are actually updated...

scott@ORA734.WORLD> update name
  2     set columnName = ( select value
  3                          from lookup
  4                         where lookup.keyname = name.keyname
  5                           and otherColumn = :other_value )
  6   where exists ( select value
  7                    from lookup
  8                   where lookup.keyname = name.keyname
  9                     and otherColumn = :other_value )
 10  /

1 row updated.

scott@ORA734.WORLD> select * from name;

   KEYNAME COLUMNNAME
---------- -------------------------
       100 New Data
       200 Original Data
 
[@more@]from

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