MODIFY COLUMN in oracle - How to check if a column is nullable before setting to nullable?
Solution 1
You could do this in PL/SQL:
declare
l_nullable user_tab_columns.nullable%type;
begin
select nullable into l_nullable
from user_tab_columns
where table_name = 'MYTABLE'
and column_name = 'MYCOLUMN';
if l_nullable = 'N' then
execute immediate 'alter table mytable modify (mycolumn null)';
end if;
end;
Solution 2
just do the alter table and catch the exception.
DECLARE
allready_null EXCEPTION;
PRAGMA EXCEPTION_INIT(allready_null, -1451);
BEGIN
execute immediate 'ALTER TABLE TAB MODIFY(COL NULL)';
EXCEPTION
WHEN allready_null THEN
null; -- handle the error
END;
/
if you don't want to use PL/SQL
set feedback off
set echo off
set feedback off
set pages 0
set head off
spool to_null.sql
select 'alter table TAB modify (COL NULL);'
from user_tab_columns
where table_name = 'TAB'
and column_name = 'COL'
and nullable = 'N';
spool off
set feedback on
set echo on
set termout on
@@to_null.sql
host rm -f to_null.sql
or just do the alter table and ignore the error.
Jay S
Dad, blogger, and speaker with over 20 years of experience in the software development field. Into Sitecore, DevOps, integrations, software architecture, and stopping slapshots.
Updated on August 24, 2020Comments
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Jay S over 3 years
I'm trying to fill in for a colleague in doing some Oracle work, and ran into a snag. In attempting to write a script to modify a column to nullable, I ran into the lovely ORA-01451 error:
ORA-01451: column to be modified to NULL cannot be modified to NULL
This is happening because the column is already NULL. We have several databases that need to be udpated, so in my faulty assumption I figured setting it to NULL should work across the board to make sure everybody was up to date, regardless of whether they had manually set this column to nullable or not. However, this apparently causes an error for some folks who already have the column as nullable.
How does one check if a column is already nullable so as to avoid the error? Something that would accomplish this idea:
IF( MyTable.MyColumn IS NOT NULLABLE) ALTER TABLE MyTable MODIFY(MyColumn NULL);