I regularly have to change the structure of some fairly large tables (~200m
rows). Often we use the opportunity to do a full table rebuild if we want
to change other settings (such as index locations) but other times we would
prefer to modify the existing table.
I currently have the scenario where I need to add a single CHAR(1) column
to a 250m row table and populate it with a constant value (new records may
have a different value). The approach I am considering is:
1) alter table blah add (mycol char(1));
2) update blah set mycol = 'F '; {perhaps include a parallel hint on
this statement}
3) alter table blah modify mycol not null enable novalidate;
I was hoping to use "enable novalidate " to avoid a verification of all
records when I know they will be populated. However I noticed that a
describe on the table produces unexpected results. Here is a demo:
SQL > desc blah
Name Null? Type
-- ---- ---- ---- ---- ---- ---- ---- ---- ---- -- -----
-- ---- ---- ---- ---- ---- ----
FIRSTCOL NUMBER
SQL > insert into blah (firstcol) values (1);
insert into blah (firstcol) values (1)
*
ERROR at line 1:
ORA-01400 (See ORA-01400.ora-code.com): cannot insert NULL into ( "SPARKY ". "BLAH ". "MYCOL ")
SQL > alter table blah modify mycol null;
Table altered.
Elapsed: 00:00:00.04
SQL > alter table blah modify mycol not null;
Table altered.
Elapsed: 00:00:00.06
SQL > desc blah;
Name Null? Type
-- ---- ---- ---- ---- ---- ---- ---- ---- ---- -- -----
-- ---- ---- ---- ---- ---- ----
FIRSTCOL NUMBER
MYCOL NOT NULL CHAR(1)
This is happening on Oracle 8.1.7.4 (running on Solaris) and is repeatable.
Whenever "enable novalidate " is used the constraint doesn 't appear. Trying
to insert null data shows the constraint is actually there, just not
appearing in describe.
Any ideas? Any workarounds? Fixed in Oracle 9 (although we are bound to 8
due to applications that connect)?
Thanks in advance,
Mark.
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