db-derby-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Mamta A. Satoor (JIRA)" <derby-...@db.apache.org>
Subject [jira] Created: (DERBY-783) Enhance ALTER TABLE syntax to allow users to change the next value to be generated for an identity column
Date Fri, 23 Dec 2005 08:14:31 GMT
Enhance ALTER TABLE syntax to allow users to change the next value to be generated for an identity
column
---------------------------------------------------------------------------------------------------------

         Key: DERBY-783
         URL: http://issues.apache.org/jira/browse/DERBY-783
     Project: Derby
        Type: New Feature
  Components: SQL  
    Versions: 10.2.0.0    
    Reporter: Mamta A. Satoor
 Assigned to: Mamta A. Satoor 


Derby allows a user to change the interval between consecutive values of the identity column
using ALTER TABLE. But there is no way to change the next value to be generated for an identity
column. Such a support in Derby will be very handy for tables with identity column defined
as GENERATED BY DEFAULT and with a unique key defined on them. Column defined with GENERATED
BY DEFAULT allows system to generate values for them or allows the user to manually supply
the value for them. A column defined this way is very useful when the user might want to import
some data into the generated column manually. But this can create problems when the system
generated values conflict with manually inserted values.

eg
autocommit on;
create table tauto(i int generated by default as identity, k int); 
create unique index tautoInd on tauto(i); 
insert into tauto(k) values 1,2;  -- let system generate values for the identity column
-- now do few manual inserts into identity column
insert into tauto values (3,3); 
insert into tauto values (4,4); 
insert into tauto values (5,5); 
insert into tauto values (6,6); 
insert into tauto values (7,7); 
insert into tauto values (8,8); 
-- notice that identity column at this point has used 1 through 8
-- now if the user wants to let the system generate a value, system will generate 3 but that
is already used and hence
-- insert will throw unique key failure exception. System has consumed 3 at this point.
insert into tauto(k) values 9;
-- the insert above will continue to fail with the unique key failure exceptions until system
has consumed all the values till 8
-- If we add ALTER TABLE syntax to allow changing the next value to be generated, then user
can simply use that to change
-- next value to be generated to 9 after the manual inserts above and then insert into tauto(k)
values 9 will not fail

SQL standard syntax for changing the next generated value
ALTER TABLE <tablename> ALTER <columnName> RESTART WITH integer-constant

-- 
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators:
   http://issues.apache.org/jira/secure/Administrators.jspa
-
For more information on JIRA, see:
   http://www.atlassian.com/software/jira


Mime
View raw message