How to set variable from a SQL query?

Question

I\'m trying to set a variable from a SQL query:

declare @ModelID uniqueidentifer

Select @ModelID = select modelid from models
where areaid = \'South Coast\'         


        

Answer 1

Use TOP 1 if the query returns multiple rows.

SELECT TOP 1 @ModelID = m.modelid 
  FROM MODELS m
 WHERE m.areaid = 'South Coast'

Answer 2

I prefer just setting it from the declare statement

DECLARE @ModelID uniqueidentifer = (SELECT modelid 
                                    FROM models
                                    WHERE areaid = 'South Coast')

Answer 3

declare @ModelID uniqueidentifer

--make sure to use brackets
set @ModelID = (select modelid from models
where areaid = 'South Coast')

select @ModelID

Answer 4

SELECT @ModelID = modelid
FROM Models
WHERE areaid = 'South Coast'

If your select statement returns multiple values, your variable is assigned the last value that is returned.

For reference on using SELECT with variables: http://msdn.microsoft.com/en-us/library/aa259186%28SQL.80%29.aspx

Answer 5

Using SELECT:

SELECT @ModelID = m.modelid 
  FROM MODELS m
 WHERE m.areaid = 'South Coast'

Using SET:

SET @ModelID = (SELECT m.modelid 
                  FROM MODELS m
                 WHERE m.areaid = 'South Coast')

See this question for the difference between using SELECT and SET in TSQL.

Warning

If this select statement returns multiple values (bad to begin with):

• When using SELECT, the variable is assigned the last value that is returned (as womp said), without any error or warning (this may cause logic bugs)
• When using SET, an error will occur

Answer 6

You can use this, but remember that your query gives 1 result, multiple results will throw the exception.

declare @ModelID uniqueidentifer
Set @ModelID = (select Top(1) modelid from models where areaid = 'South Coast')

Another way:

Select Top(1)@ModelID = modelid from models where areaid = 'South Coast'