Assign exec parameter in a variable using sql query

//////////Funtions/////////

declare @Variable varchar(12)

declare @SqtCommand nvarchar(4000)

set @SqtCommand = 'select @Variable= FiledName from TableName'

exec sp_executeSQl @SqtCommand, N'@Variable varchar(12) output', @Variable output

print @Variable

//////////RESULT////////////

declare @Variable varchar(12)

declare @SqtCommand nvarchar(4000)

set @SqtCommand = 'select @Variable=CAST(MIN(Year)as varchar)+''-''+ cast(MAX(Year) as varchar) from tbl_SurfaceWater inner join mstLocation on tbl_SurfaceWater.LocationGUID=mstLocation.LocationGUID where (Year(GETDATE())-Year) between 0 and 30 and DataTypeCatID=1 and TemplateID=2'

exec sp_executeSQl @SqtCommand, N'@Variable varchar(12) output', @Variable output

print @Variable

/////////Result///////////