Sql – Restrict varchar() column to specific values

sqlsql-server-2008ssms

Is there a way to specify, for example 4 distinct values for a varchar column in MS SQL Server 2008?

For example, I need a column called Frequency (varchar) that only accepts 'Daily', 'Weekly', 'Monthly', 'Yearly' as possible values

Is this possible to set within the SQL Server Management Studio when creating the table?

Best Answer

Have you already looked at adding a check constraint on that column which would restrict values? Something like:

CREATE TABLE SomeTable
(
   Id int NOT NULL,
   Frequency varchar(200),
   CONSTRAINT chk_Frequency CHECK (Frequency IN ('Daily', 'Weekly', 'Monthly', 'Yearly'))
)

Syntax:

ALTER TABLE {TABLENAME} 
ADD {COLUMNNAME} {TYPE} {NULL|NOT NULL} 
CONSTRAINT {CONSTRAINT_NAME} DEFAULT {DEFAULT_VALUE}
WITH VALUES

Example:

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.

Notes:

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.

Best Answer

Related Solutions

Sql – Insert into … values ( SELECT … FROM … )

Sql – Add a column with a default value to an existing table in SQL Server

Syntax:

Example:

Notes:

Related Topic