-- 基本语法
function_name(args) OVER (
    [PARTITION BY partition_expression]
    [ORDER BY sort_expression [ASC|DESC] [NULLS {FIRST|LAST}]]
    [frame_clause]
)

-- 窗口帧子句
ROWS BETWEEN frame_start AND frame_end
RANGE BETWEEN frame_start AND frame_end
GROUPS BETWEEN frame_start AND frame_end

-- frame_start / frame_end 选项
UNBOUNDED PRECEDING   -- 分区开始
N PRECEDING           -- 当前行前 N 行
CURRENT ROW          -- 当前行
N FOLLOWING          -- 当前行后 N 行
UNBOUNDED FOLLOWING  -- 分区结束

-- 默认窗口帧
-- 有 ORDER BY: RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
-- 无 ORDER BY: ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING