How to convert rows in to column

--How to get ids in one line usign , Delimeted 

DECLARE @planids TABLE (Id INT)

INSERT INTO @planids VALUES (123),(234),(343),(543),(45345),(543),(4534)

SELECT * FROM @planids

DECLARE @plans varchar(max)

SET @plans = ''

SELECT  @plans = @plans+ cast(Id AS varchar(12)) +',  '

FROM @planids 

--where ParentPlanId in (373289)

SELECT @plans AS PlanList