How can I add a column with a default value to an existing table in SQL Server 2000 / SQL Server 2005?
This is for SQL Server:
ALTER TABLE TableName
ADD ColumnName (type) -- NULL OR NOT NULL
DEFAULT (default value)
WITH VALUES
Example:
ALTER TABLE Activities
ADD status int NOT NULL DEFAULT (0)
WITH VALUES
If you want to add constraints then:
ALTER TABLE Table_1
ADD row3 int NOT NULL
CONSTRAINT CONSTRAINT_NAME DEFAULT (0)
WITH VALUES
ALTER TABLE {TABLENAME}
ADD {COLUMNNAME} {TYPE} {NULL|NOT NULL}
CONSTRAINT {CONSTRAINT_NAME} DEFAULT {DEFAULT_VALUE}
WITH VALUES
ALTER TABLE SomeTable
ADD SomeCol Bit NULL --Or NOT NULL.
CONSTRAINT D_SomeTable_SomeCol --When Omitted a Default-Constraint Name is autogenerated.
DEFAULT (0)--Optional Default-Constraint.
WITH VALUES --Add if Column is Nullable and you want the Default Value for Existing Records.
Optional Constraint Name:
If you leave out CONSTRAINT D_SomeTable_SomeCol
then SQL Server will autogenerate
a Default-Contraint with a funny Name like: DF__SomeTa__SomeC__4FB7FEF6
Optional With-Values Statement:
The WITH VALUES
is only needed when your Column is Nullable
and you want the Default Value used for Existing Records.
If your Column is NOT NULL
, then it will automatically use the Default Value
for all Existing Records, whether you specify WITH VALUES
or not.
How Inserts work with a Default-Constraint:
If you insert a Record into SomeTable
and do not Specify SomeCol
's value, then it will Default to 0
.
If you insert a Record and Specify SomeCol
's value as NULL
(and your column allows nulls),
then the Default-Constraint will not be used and NULL
will be inserted as the Value.
Notes were based on everyone's great feedback below.
Special Thanks to:
@Yatrix, @WalterStabosz, @YahooSerious, and @StackMan for their Comments.
ALTER TABLE <table name>
ADD <new column name> <data type> NOT NULL
GO
ALTER TABLE <table name>
ADD CONSTRAINT <constraint name> DEFAULT <default value> FOR <new column name>
GO
This has a lot of answers, but I feel the need to add this extended method. This seems a lot longer, but it is extremely useful if you're adding a NOT NULL field to a table with millions of rows in an active database.
ALTER TABLE {schemaName}.{tableName}
ADD {columnName} {datatype} NULL
CONSTRAINT {constraintName} DEFAULT {DefaultValue}
UPDATE {schemaName}.{tableName}
SET {columnName} = {DefaultValue}
WHERE {columName} IS NULL
ALTER TABLE {schemaName}.{tableName}
ALTER COLUMN {columnName} {datatype} NOT NULL
What this will do is add the column as a nullable field and with the default value, update all fields to the default value (or you can assign more meaningful values), and finally it will change the column to be NOT NULL.
The reason for this is if you update a large scale table and add a new not null field it has to write to every single row and hereby will lock out the entire table as it adds the column and then writes all the values.
This method will add the nullable column which operates a lot faster by itself, then fills the data before setting the not null status.
I've found that doing the entire thing in one statement will lock out one of our more active tables for 4-8 minutes and quite often I have killed the process. This method each part usually takes only a few seconds and causes minimal locking.
Additionally, if you have a table in the area of billions of rows it may be worth batching the update like so:
WHILE 1=1
BEGIN
UPDATE TOP (1000000) {schemaName}.{tableName}
SET {columnName} = {DefaultValue}
WHERE {columName} IS NULL
IF @@ROWCOUNT < 1000000
BREAK;
END
When adding a nullable column, WITH VALUES
will ensure that the specific DEFAULT value is applied to existing rows:
ALTER TABLE table
ADD column BIT -- Demonstration with NULL-able column added
CONSTRAINT Constraint_name DEFAULT 0 WITH VALUES
In SQL Server 2008-R2, I go to the design mode - in a test database - and add my two columns using the designer and made the settings with the GUI, and then the infamous Right-Click gives the option "Generate Change Script"!
Bang up pops a little window with, you guessed it, the properly formatted guaranteed-to-work change script. Hit the easy button.