.........
      select string_value from stock_vars var1
       where task.stock_id = var1.stock_id
        and var1.alias = 'stockitId'
      ) as STOCKID
      ,(
      select string_value from stock_vars var1
       where task.stock_id = var1.stock_id
        and var1.alias = 'stocktNumber'
      ) as STOCKNUMBER
     ,(
      select string_value from stock_vars var1
       where task.stock_id = var1.stock_id
        and var1.alias = 'stockTitle'
      ) as STOCKTTITLE 
     ,(
     .......

;WITH [dbo.vwStockVars] AS (	-- Сразу VIEW сделать и не парится потом
	SELECT	S.stock_id
		-- alias строковый - это изврат, там должен быть его ID, а названия хранятся в справочнике. Про 3ю нормальную форму слышал?
		-- string_value - Про SQL_Variant не слышал?
	,	Max(CASE WHEN S.alias = 'stockitId'	THEN S.string_value END)	AS stockitId
	,	Max(CASE WHEN S.alias = 'stocktNumber'	THEN S.string_value END)	AS stocktNumber
	,	Max(CASE WHEN S.alias = 'stockTitle'	THEN S.string_value END)	AS stockTitle
	FROM	dbo.Stock_Vars	S	-- CamelCase вааще-то стандарт: stock_vars -> StockVars, string_value -> StringValue
	GROUP BY S.stock_id
)	SELECT	*
	FROM	dbo.Task		T
LEFT	JOIN	[dbo.vwStockVars]	V ON V.stock_id = T.stock_id