insert a NOT NULL column to an existing table
As an option you can initially create Null-able column, then update your table column with valid not null values and finally ALTER column to set NOT NULL constraint:
ALTER TABLE MY_TABLE ADD STAGE INT NULL
GO
UPDATE MY_TABLE SET <a valid not null values for your column>
GO
ALTER TABLE MY_TABLE ALTER COLUMN STAGE INT NOT NULL
GO
Another option is to specify correct default value for your column:
ALTER TABLE MY_TABLE ADD STAGE INT NOT NULL DEFAULT '0'
UPD: Please note that answer above contains GO
which is a must when you run this code on Microsoft SQL server. If you want to perform the same operation on Oracle or MySQL you need to use semicolon ;
like that:
ALTER TABLE MY_TABLE ADD STAGE INT NULL;
UPDATE MY_TABLE SET <a valid not null values for your column>;
ALTER TABLE MY_TABLE ALTER COLUMN STAGE INT NOT NULL;
If you aren't allowing the column to be Null you need to provide a default to populate existing rows. e.g.
ALTER TABLE dbo.YourTbl ADD
newcol int NOT NULL CONSTRAINT DF_YourTbl_newcol DEFAULT 0
On Enterprise Edition this is a metadata only change since 2012