小编Wil*_*m R的帖子

我需要根据 session_id 计算 Postgres 中前一天累积值的差异。示例如下：

CREATE TEMP TABLE foo AS
SELECT date::date, session_id, upload_usage, download_usage, total_usage_on_a_day
FROM ( VALUES
  ( '10/21/2014', '0007994b', 37578561   , 6800209   , 44378770 ),
  ( '10/22/2014', '0007994b', 218113296  , 85272007  , 303385303 ),
  ( '10/23/2014', '0007994b', 552228616  , 252390680 , 804619296 ) ,
  ( '10/24/2014', '0007994b', 799772020  , 391196041 , 1190968061 ),
  ( '10/25/2014', '0007994b', 1047233978 , 529908804 , 1577142782 ),
  ( '10/26/2014', '0007994b', 1294608258 , 668515778 , 1963124036 ),
  ( '10/27/2014', '0007994b', 1066656794 , 557318645 …