CODEWITHSUNDEEP
sqloracle-databasealter-table
ravi
ravi

Reputation: 1827

Alter table to modify default value of column

I have a requirement where we need to modify a column's default value in database table. The table is already an existing table in database and currently the default value of the column is NULL. Now if add a new default value to this column, If I am correct it updates all the existing NULLs of the column to new DEfault value. Is there a way to not to do this but still set a new default value on column. I mean I do not want the existing NULLs to be updated and want them to remain as NULLs.

Any help on this is appreciated. Thanks

Upvotes: 43

Views: 293245

Answers (6)

skk
skk

Reputation: 161

ALTER TABLE *table_name*
MODIFY *column_name* DEFAULT *value*;

worked in Oracle

e.g:

ALTER TABLE MY_TABLE
MODIFY MY_COLUMN DEFAULT 1;

Upvotes: 11

VGoudkov
VGoudkov

Reputation: 31

ALTER TABLE <table_name> MODIFY <column_name> DEFAULT <defult_value>

EX: ALTER TABLE AAA MODIFY ID DEFAULT AAA_SEQUENCE.nextval

Tested on Oracle Database 12c Enterprise Edition Release 12.2.0.1.0

Upvotes: 3

Prema Arya
Prema Arya

Reputation: 69

For Sql Azure the following query works :

ALTER TABLE [TableName] ADD  DEFAULT 'DefaultValue' FOR ColumnName
GO

Upvotes: -2

amit kumar
amit kumar

Reputation: 21032

Following Justin's example, the command below works in Postgres:

alter table foo alter column col2 set default 'bar';

Upvotes: 2

Pankaj Kumar
Pankaj Kumar

Reputation: 47

ALTER TABLE {TABLE NAME}
ALTER COLUMN {COLUMN NAME} SET DEFAULT '{DEFAULT VALUES}'

example :

ALTER TABLE RESULT
ALTER COLUMN STATUS SET DEFAULT 'FAIL'

Upvotes: 2

Justin Cave
Justin Cave

Reputation: 231671

Your belief about what will happen is not correct. Setting a default value for a column will not affect the existing data in the table.

I create a table with a column col2 that has no default value

SQL> create table foo(
  2    col1 number primary key,
  3    col2 varchar2(10)
  4  );

Table created.

SQL> insert into foo( col1 ) values (1);

1 row created.

SQL> insert into foo( col1 ) values (2);

1 row created.

SQL> insert into foo( col1 ) values (3);

1 row created.

SQL> select * from foo;

      COL1 COL2
---------- ----------
         1
         2
         3

If I then alter the table to set a default value, nothing about the existing rows will change

SQL> alter table foo
  2    modify( col2 varchar2(10) default 'foo' );

Table altered.

SQL> select * from foo;

      COL1 COL2
---------- ----------
         1
         2
         3

SQL> insert into foo( col1 ) values (4);

1 row created.

SQL> select * from foo;

      COL1 COL2
---------- ----------
         1
         2
         3
         4 foo

Even if I subsequently change the default again, there will still be no change to the existing rows

SQL> alter table foo
  2    modify( col2 varchar2(10) default 'bar' );

Table altered.

SQL> select * from foo;

      COL1 COL2
---------- ----------
         1
         2
         3
         4 foo

SQL> insert into foo( col1 ) values (5);

1 row created.

SQL> select * from foo;

      COL1 COL2
---------- ----------
         1
         2
         3
         4 foo
         5 bar

Upvotes: 74

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