I am trying to add a new column into an existing table, which has to be NOT NULL. It is a foreign key referring to ID of other table and I can't use default value.
I did it in couple of steps:
add the new column to the table with NULL constraint
run update scripts to update the new column with correct values for all rows
add foreign key constraint
change the new column to NOT NULL
The issue is that I want to follow a rule we have, that the DDL and DML scripts are separated (for couple of reasons). I can't figure out how to do this. Is there a way how to add a NOT NULL column into an existing table in a way that the DDL and DML would be separated?
Do step 1 and 3 together (if you do not then you risk adding values in step 2 that will not match the constraint).
ALTER TABLE table_name
ADD column_name NUMBER(8,0)
CONSTRAINT table_name__column_name__fk REFERENCES other_table(other_column);
You can also do step 4 at the same time if you make the NOT NULL constraint DEFERRABLE:
ALTER TABLE table_name
ADD column_name NUMBER(8,0)
CONSTRAINT table_name__column_name__nn NOT NULL DEFERRABLE
CONSTRAINT table_name__column_name__fk REFERENCES other_table(other_column);
Then update the data. For example, you can use a MERGE statement to update from a sub-query of pre-generated values:
MERGE INTO table_name dst
USING (
SELECT 1 AS id, 2 AS new_column_name FROM DUAL UNION ALL
SELECT 2, 2 FROM DUAL UNION ALL
SELECT 3, 1 FROM DUAL UNION ALL
SELECT 4, 4 FROM DUAL
) src
ON (dst.id = src.id)
WHEN MATCHED THEN
UPDATE
SET column_name = src.new_column_name;
Then:
COMMIT;
Which will enforce any DEFERRABLE NOT NULL constraints.
If you did not make the constraint DEFERRABLE
then change the column to NOT NULL:
ALTER TABLE table_name
MODIFY column_name NUMBER(8,0) NOT NULL;
db<>fiddle (not deferrable) (deferrable)
Related
I was wondering how can I add an identity column to existing oracle table? I am using oracle 11g. Suppose I have a table named DEGREE and I am going to add an identity column to that.
FYI table is not empty.
You can not do it in one step. Instead,
Alter the table and add the column (without primary key constraint)
ALTER TABLE DEGREE ADD (Ident NUMBER(10));
Fill the new column with data which will fulfill the primary key constraint (unique/not null), e.g. like
UPDATE DEGREE SET Ident=ROWNUM;
Alter the table and add the constraint to the column
ALTER TABLE DEGREE MODIFY (Ident PRIMARY KEY);
After that is done, you can set up a SEQUENCE and a BEFORE INSERT trigger to automatically set the id value for new records.
From Oracle 12c you would use an identity column.
For example, say your table is called demo and has 3 columns and 100 rows:
create table demo (col1, col2, col3)
as
select dbms_random.value(1,10), dbms_random.value(1,10), dbms_random.value(1,10)
from dual connect by rownum <= 100;
You could add an identity column using:
alter table demo add demo_id integer generated by default on null as identity;
update demo set demo_id = rownum;
Then reset the internal sequence to match the data and prevent manual inserts:
alter table demo modify demo_id generated always as identity start with limit value;
and define it as the primary key:
alter table demo add constraint demo_pk primary key (demo_id);
This leaves the new column at the end of the column list, which shouldn’t normally matter (except for tables with a large number of columns and row chaining issues), but it looks odd when you describe the table. However, we can at least tidy up the dictionary order using the invisible/visible hack:
SQL> desc demo
Name Null? Type
-------------------------------- -------- ----------------------
COL1 NUMBER
COL2 NUMBER
COL3 NUMBER
DEMO_ID NOT NULL NUMBER(38)
begin
for r in (
select column_name from user_tab_columns c
where c.table_name = 'DEMO'
and c.column_name <> 'DEMO_ID'
order by c.column_id
)
loop
execute immediate 'alter table demo modify '||r.column_name||' invisible';
execute immediate 'alter table demo modify '||r.column_name||' visible';
end loop;
end;
/
SQL> desc demo
Name Null? Type
-------------------------------- -------- ----------------------
DEMO_ID NOT NULL NUMBER(38)
COL1 NUMBER
COL2 NUMBER
COL3 NUMBER
One thing you can't do (as of Oracle 18.0) is alter an existing column to make it into an identity column, so you have to either go through a process like the one above but copying the existing values and finally dropping the old column, or else define a new table explicitly with the identity column in place and copy the data across in a separate step. Otherwise you'll get:
-- DEMO_ID column exists but is currently not an identity column:
alter table demo modify demo_id generated by default on null as identity start with limit value;
-- Fails with:
ORA-30673: column to be modified is not an identity column
add the column
alter table table_name add (id INTEGER);
create a sequence table_name_id_seq with start with clause, using number of rows in the table + 1 or another safe value(we don't want duplicate ids);
lock the table (no inserts)
alter table table_name lock exclusive mode;
fill the column
update table_name set id = rownum; --or another logic
add a trigger to automaticaly put the id on insert using the sequence(you can find examples on internet, for example this answer)
When you'll fire the create trigger the lock will be released. (it automatically commits).
Also, you may add unique constraint on the id column, it is best to do so.
For Oracle :
CREATE TABLE new_table AS (SELECT ROWNUM AS id, ta.* FROM old_table ta)
remember this id column is not auto incremented
we are confused with below answers.so our answer is 3, 5
Which three actions can you perform by using the ALTER TABLE command?
1- Lock a set of rows in a table.
2- Drop pseudocolumns from a table.
3- Rename a table.
4- Drop all columns simultaneously from a table.
5- Enable or disable constraints on a table.
6- Restrict all DML statements on a table.
Thank you
3, 5 and 6
Lock a set of rows in a table.
Oracle locks rows it is performing DML on or when you use SELECT ... FOR UPDATE; you cannot lock rows with ALTER TABLE.
Drop pseudocolumns from a table.
The common pseudocolumns of a table are ROWID, ROWNUM and ORA_ROWSCN; you cannot drop these.
Rename a table.
CREATE TABLE table_name ( a NUMBER, b NUMBER );
ALTER TABLE table_name RENAME TO other_name;
Works.
Drop all columns simultaneously from a table.
CREATE TABLE table_name ( a NUMBER, b NUMBER );
ALTER TABLE table_name DROP ( a, b );
Outputs:
ORA-12983: cannot drop all columns in a table
Enable or disable constraints on a table.
CREATE TABLE table_name ( a NUMBER CONSTRAINT qu5__pk PRIMARY KEY, b NUMBER );
ALTER TABLE table_name MODIFY PRIMARY KEY DISABLE;
Will disable the constraint.
Restrict all DML statements on a table.
CREATE TABLE table_name ( a NUMBER, b NUMBER );
ALTER TABLE table_name READ ONLY;
Then
INSERT INTO table_name ( a, b ) VALUES ( 1, 1 );
UPDATE table_name SET b = 2;
DELETE FROM table_name;
all fail with the exception:
ORA-12081: update operation not allowed on table "SCHEMA_NAME"."TABLE_NAME"
db<>fiddle here
How to make a NULLable column (varchar2(20)) to NOT NULL of a table in oracle where I have more than 1 million records in the table
NOT NULL constraint specifies that a column cannot contain NULL values. To add a NOT NULL constraint to an existing table by using the ALTER TABLE statement.
ALTER TABLE table_name MODIFY ( column_name NOT NULL);
In this case, the column_name must not contain any NULL value before applying the NOT NULL constraint.
I'd like to add a NOT NULL column to a Redshift table that has records, an IDENTITY field, and that other tables have foreign keys to.
In PostgreSQL, you can add the column as NULL, fill it in, then ALTER it to be NOT NULL.
In Redshift, the best I've found so far is:
ALTER TABLE my_table ADD COLUMN new_column INTEGER;
-- Fill that column
CREATE TABLE my_table2 (
id INTEGER IDENTITY NOT NULL SORTKEY,
(... all the fields ... )
new_column INTEGER NOT NULL,
PRIMARY KEY(id)
) DISTSTYLE all;
UNLOAD ('select * from my_table')
to 's3://blah' credentials '<aws-auth-args>' ;
COPY my_table2
from 's3://blah' credentials '<aws-auth-args>'
EXPLICIT_IDS;
DROP table my_table;
ALTER TABLE my_table2 RENAME TO my_table;
-- For each table that had a foreign key to my_table:
ALTER TABLE another_table ADD FOREIGN KEY(my_table_id) REFERENCES my_table(id)
Is this the best way of achieving this?
You can achieve this w/o having to load to S3.
modify the existing table to create the desired column w/ a default value
update that column in some way (in my case it was copying from another column)
create a new table with the column w/o a default value
insert into the new table (you must list out the columns rather than using (*) since the order may be the same (say if you want the new column in position 2)
drop the old table
rename the table
alter table to give correct owner (if appropriate)
ex:
-- first add the column w/ a default value
alter table my_table_xyz
add visit_id bigint NOT NULL default 0; -- not null but default value
-- now populate the new column with whatever is appropriate (the key in my case)
update my_table_xyz
set visit_id = key;
-- now create the new table with the proper constraints
create table my_table_xzy_new
(
key bigint not null,
visit_id bigint NOT NULL, -- here it is not null and no default value
adt_id bigint not null
);
-- select all from old into new
insert into my_table_xyz_new
select key, visit_id, adt_id
from my_table_xyz;
-- remove the orig table
DROP table my_table_xzy_events;
-- rename the newly created table to the desired table
alter table my_table_xyz_new rename to my_table_xyz;
-- adjust any views, foreign keys or permissions as required
I have a table in Oracle with several constraints. When I insert a new record and not all constraints are valid, then Oracle raise only the "first" error. How to get all violations of my record?
CREATE TABLE A_TABLE_TEST (
COL_1 NUMBER NOT NULL,
COL_2 NUMBER NOT NULL,
COL_3 NUMBER NOT NULL,
COL_4 NUMBER NOT NULL
);
INSERT INTO A_TABLE_TEST values (1,null,null,2);
ORA-01400: cannot insert NULL into ("USER_4_8483C"."A_TABLE_TEST"."COL_2")
I would like to get something like this:
Column COL_2: cannot insert NULL
Column COL_3: cannot insert NULL
This would be also sufficient:
Column COL_2: not valid
Column COL_3: not valid
Of course I could write a trigger and check each column individually, but I like to prefer constraints rather than triggers, they are easier to maintain and don't require manually written code.
Any idea?
There no straightforward way to report all possible constraint violations. Because when Oracle stumble on first violation of a constraint, no further evaluation is possible, statement fails, unless that constraint is deferred one or the log errors clause has been included in the DML statement. But it should be noted that log errors clause won't be able to catch all possible constraint violations, just records first one.
As one of the possible ways is to:
create exceptions table. It can be done by executing ora_home/rdbms/admin/utlexpt.sql script. The table's structure is pretty simple;
disable all table constraints;
execute DMLs;
enable all constraints with exceptions into <<exception table name>> clause. If you executed utlexpt.sql script, the name of the table exceptions are going to be stored would be exceptions.
Test table:
create table t1(
col1 number not null,
col2 number not null,
col3 number not null,
col4 number not null
);
Try to execute an insert statement:
insert into t1(col1, col2, col3, col4)
values(1, null, 2, null);
Error report -
SQL Error: ORA-01400: cannot insert NULL into ("HR"."T1"."COL2")
Disable all table's constraints:
alter table T1 disable constraint SYS_C009951;
alter table T1 disable constraint SYS_C009950;
alter table T1 disable constraint SYS_C009953;
alter table T1 disable constraint SYS_C009952;
Try to execute the previously failed insert statement again:
insert into t1(col1, col2, col3, col4)
values(1, null, 2, null);
1 rows inserted.
commit;
Now, enable table's constraints and store exceptions, if there are any, in the exceptions table:
alter table T1 enable constraint SYS_C009951 exceptions into exceptions;
alter table T1 enable constraint SYS_C009950 exceptions into exceptions;
alter table T1 enable constraint SYS_C009953 exceptions into exceptions;
alter table T1 enable constraint SYS_C009952 exceptions into exceptions;
Check the exceptions table:
column row_id format a30;
column owner format a7;
column table_name format a10;
column constraint format a12;
select *
from exceptions
ROW_ID OWNER TABLE_NAME CONSTRAINT
------------------------------ ------- ------- ------------
AAAWmUAAJAAAF6WAAA HR T1 SYS_C009951
AAAWmUAAJAAAF6WAAA HR T1 SYS_C009953
Two constraints have been violated. To find out column names, simply refer to user_cons_columns data dictionary view:
column table_name format a10;
column column_name format a7;
column row_id format a20;
select e.table_name
, t.COLUMN_NAME
, e.ROW_ID
from user_cons_columns t
join exceptions e
on (e.constraint = t.constraint_name)
TABLE_NAME COLUMN_NAME ROW_ID
---------- ---------- --------------------
T1 COL2 AAAWmUAAJAAAF6WAAA
T1 COL4 AAAWmUAAJAAAF6WAAA
The above query gives us column names, and rowids of problematic records. Having rowids at hand, there should be no problem to find those records that cause constraint violation, fix them, and re-enable constraints once again.
Here is the script that has been used to generate alter table statements for enabling and disabling constraints:
column cons_disable format a50
column cons_enable format a72
select 'alter table ' || t.table_name || ' disable constraint '||
t.constraint_name || ';' as cons_disable
, 'alter table ' || t.table_name || ' enable constraint '||
t.constraint_name || ' exceptions into exceptions;' as cons_enable
from user_constraints t
where t.table_name = 'T1'
order by t.constraint_type
You would have to implement a before-insert trigger to loop through all the conditions that you care about.
Think about the situation from the database's perspective. When you do an insert, the database can basically do two things: complete the insert successfully or fail for some reason (typically a constraint violation).
The database wants to proceed as quickly as possibly and not do unnecessary work. Once it has found the first complaint violation, it knows that the record is not going into the database. So, the engine wisely returns an error and stops checking further constraints. There is no reason for the engine to get the full list of violations.
In the meantime I found a lean solution using deferred constraints:
CREATE TABLE A_TABLE_TEST (
COL_1 NUMBER NOT NULL DEFERRABLE INITIALLY DEFERRED,
COL_2 NUMBER NOT NULL DEFERRABLE INITIALLY DEFERRED,
COL_3 NUMBER NOT NULL DEFERRABLE INITIALLY DEFERRED,
COL_4 NUMBER NOT NULL DEFERRABLE INITIALLY DEFERRED
);
INSERT INTO A_TABLE_TEST values (1,null,null,2);
DECLARE
CHECK_CONSTRAINT_VIOLATED EXCEPTION;
PRAGMA EXCEPTION_INIT(CHECK_CONSTRAINT_VIOLATED, -2290);
REF_CONSTRAINT_VIOLATED EXCEPTION;
PRAGMA EXCEPTION_INIT(REF_CONSTRAINT_VIOLATED , -2292);
CURSOR CheckConstraints IS
SELECT TABLE_NAME, CONSTRAINT_NAME, COLUMN_NAME
FROM USER_CONSTRAINTS
JOIN USER_CONS_COLUMNS USING (TABLE_NAME, CONSTRAINT_NAME)
WHERE TABLE_NAME = 'A_TABLE_TEST'
AND DEFERRED = 'DEFERRED'
AND STATUS = 'ENABLED';
BEGIN
FOR aCon IN CheckConstraints LOOP
BEGIN
EXECUTE IMMEDIATE 'SET CONSTRAINT '||aCon.CONSTRAINT_NAME||' IMMEDIATE';
EXCEPTION
WHEN CHECK_CONSTRAINT_VIOLATED OR REF_CONSTRAINT_VIOLATED THEN
DBMS_OUTPUT.PUT_LINE('Constraint '||aCon.CONSTRAINT_NAME||' at Column '||aCon.COLUMN_NAME||' violated');
END;
END LOOP;
END;
It works with any check constraint (not only NOT NULL). Checking FOREIGN KEY Constraint should work as well.
Add/Modify/Delete of constraints does not require any further maintenance.