SET NOCOUNT ON

DECLARE @nAmount INT
DECLARE @nCharId INT
DECLARE @nItemType INT

SET @nItemType = 14543
SET @nAmount = NULL
SET @nAmount = NULL


SELECT @nAmount = SUM(amount), @nCharId = char_id FROM user_item WHERE item_type = @nItemType GROUP BY char_id

UPDATE user_item SET amount = @nAmount WHERE char_id = @nCharId

GO