Can I create a named default constraint in an add column statement in SQL Server?

Solution 1:

This should work:

ALTER TABLE t_tableName 
    ADD newColumn VARCHAR(50)
    CONSTRAINT YourContraintName DEFAULT '' NOT NULL

Solution 2:

ALTER TABLE t_tableName 
    ADD newColumn int NOT NULL
        CONSTRAINT DF_defaultvalue DEFAULT (1)

Solution 3:

I would like to add some details:

The most important hint is: You should never-ever create a constraint without an explicit name!

The biggest problem with unnamed constraints: When you execute this on various customer machines, you will get different/random names on each.
Any future upgrade script will be a real headache...

The general advise is:

• No constraint without a name!
• Use some naming convention e.g.
  • DF_TableName_ColumnName for a default constraint
  • CK_TableName_ColumnName for a check constraint
  • UQ_TableName_ColumnName for a unique constraint
  • PK_TableName for a primary key constraint

The general syntax is

TheColumn <DataType> Nullability CONSTRAINT ConstraintName <ConstraintType> <ConstraintDetails>

Try this here

You can add more constraints to each column and you can add additional constraints just as you add columns after a comma:

CREATE TABLE dbo.SomeOtherTable(TheIdThere INT NOT NULL CONSTRAINT PK_SomeOtherTable PRIMARY KEY)
GO
CREATE TABLE dbo.TestTable
(
 --define the primary key
 ID INT IDENTITY NOT NULL CONSTRAINT PK_TestTable PRIMARY KEY

 --let the string be unique (results in a unique index implicitly)
,SomeUniqueString VARCHAR(100) NOT NULL CONSTRAINT UQ_TestTable_SomeUniqueString UNIQUE

 --define two constraints, one for a default value and one for a value check
,SomeNumber INT NULL CONSTRAINT DF_TestTable_SomeNumber DEFAULT (0)
                     CONSTRAINT CK_TestTable_SomeNumber_gt100 CHECK(SomeNumber>100)

 --add a foreign key constraint
,SomeFK INT NOT NULL CONSTRAINT FK_TestTable_SomeFK FOREIGN KEY REFERENCES dbo.SomeOtherTable(TheIdThere)

 --add a constraint for two columns separately
,CONSTRAINT UQ_TestTable_StringAndNumber UNIQUE(SomeFK,SomeNumber)
);
GO

--insert some data

INSERT INTO dbo.SomeOtherTable VALUES(1);
INSERT INTO dbo.TestTable(SomeUniqueString,SomeNumber,SomeFK) VALUES('hello',111,1);
GO
INSERT INTO dbo.TestTable(SomeUniqueString,SomeNumber,SomeFK) 
VALUES('fails due to uniqueness of 111,1',111,1);

Solution 4:

Try like below script-

ALTER TABLE DEMO_TABLE
ADD Column1 INT CONSTRAINT Def_Column1 DEFAULT(3) NOT NULL,
    Column2 VARCHAR(10) CONSTRAINT Def_Column2 DEFAULT('New') NOT NULL;
GO