How to set variable from a SQL query?
SqlSql ServerTsqlSql Problem Overview
I'm trying to set a variable from a SQL query:
declare @ModelID uniqueidentifer
Select @ModelID = select modelid from models
where areaid = 'South Coast'
Obviously I'm not doing this right as it doesn't work. Can somebody suggest a solution?
Thanks!
Sql Solutions
Solution 1 - Sql
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
Solution 2 - Sql
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
Solution 3 - Sql
declare @ModelID uniqueidentifer
--make sure to use brackets
set @ModelID = (select modelid from models
where areaid = 'South Coast')
select @ModelID
Solution 4 - Sql
I prefer just setting it from the declare statement
DECLARE @ModelID uniqueidentifer = (SELECT modelid
FROM models
WHERE areaid = 'South Coast')
Solution 5 - Sql
Use TOP 1 if the query returns multiple rows.
SELECT TOP 1 @ModelID = m.modelid
FROM MODELS m
WHERE m.areaid = 'South Coast'
Solution 6 - Sql
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'
Solution 7 - Sql
There are three approaches:
Below query details the advantage and disadvantage of each:
-- First way,
DECLARE @test int = (SELECT 1)
, @test2 int = (SELECT a from (values (1),(2)) t(a)) -- throws error
-- advantage: declare and set in the same place
-- Disadvantage: can be used only during declaration. cannot be used later
-- Second way
DECLARE @test int
, @test2 int
SET @test = (select 1)
SET @test2 = (SELECT a from (values (1),(2)) t(a)) -- throws error
-- Advantage: ANSI standard.
-- Disadvantage: cannot set more than one variable at a time
-- Third way
DECLARE @test int, @test2 int
SELECT @test = (select 1)
,@test2 = (SELECT a from (values (1),(2)) t(a)) -- throws error
-- Advantage: Can set more than one variable at a time
-- Disadvantage: Not ANSI standard
Solution 8 - Sql
Select @ModelID =m.modelid
From MODELS m
Where m.areaid = 'South Coast'
In this case if you have two or more results returned then your result is the last record. So be aware of this if you might have two more records returned as you might not see the expected result.
Solution 9 - Sql
#To ASSIGN variables using a SQL select the best practice is as shown below#
->DECLARE co_id INT ;
->DECLARE sname VARCHAR(10) ;
->SELECT course_id INTO co_id FROM course_details ;
->SELECT student_name INTO sname FROM course_details;
###IF you have to assign more than one variable in a single line you can use this same SELECT INTO ###
->DECLARE val1 int;
->DECLARE val2 int;
->SELECT student__id,student_name INTO val1,val2 FROM student_details;
--HAPPY CODING--