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?
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You want a check constraint.
CHECK constraints determine the valid values from a logical expression that is not based on data in another column. For example, the range of values for a salary column can be limited by creating a CHECK constraint that allows for only data that ranges from $15,000 through $100,000. This prevents salaries from being entered beyond the regular salary range.
You want something like:
ALTER TABLE dbo.Table ADD CONSTRAINT CK_Table_Frequency
CHECK (Frequency IN ('Daily', 'Weekly', 'Monthly', 'Yearly'))
You can also implement check constraints with scalar functions, as described in the link above, which is how I prefer to do it.
When you are editing a table
Right Click -> Check Constraints -> Add -> Type something like Frequency IN ('Daily', 'Weekly', 'Monthly', 'Yearly')
in expression field and a good constraint name in (Name) field.
You are done.
Personally, I'd code it as tinyint and:
Reasons:
It will take on average 8 bytes to store text, 1 byte for tinyint. Over millions of rows, this will make a difference.
What about collation? Is "Daily" the same as "DAILY"? It takes resources to do this kind of comparison.
Finally, what if you want to add "Biweekly" or "Hourly"? This requires a schema change when you could just add new rows to a lookup table.
Source: Stackoverflow.com