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一、PostgreSQL比较两天时间相减

select date_part('day', cast(now() as TIMESTAMP)- cast('2022-01-23 23:00:00'::date as TIMESTAMP));

二、PostgreSQL计算两天的天数，四舍五入

SELECT round(CAST(extract(epoch FROM(to_timestamp('2022-03-09 12:00:00','yyyy-MM-dd HH24:mi:ss') -
                                     to_timestamp('2022-03-08 00:00:00','yyyy-MM-dd HH24:mi:ss'))) /
                  (24 * 60 * 60) AS NUMERIC)
            ,0);

三、PostgreSQL天数相减得到整数

执行SQL：

select to_number(
           date_trunc('day'
                     ,'2023-09-14 01:35:00'::TIMESTAMP - 
                      '2023-09-10 01:35:00'::TIMESTAMP +
                      INTERVAL '1 day')::text
       ,'9999999999999') as s1;

执行结果：