使用Window Function超前或滞后将数据从后续行（超前）或前一行（滞后）“合并”到当前行。在这种情况下，我使用滞后函数来获得“昨天”的值。

select product, yesterday,  today, today-yesterday delta
  from ( select p.product, p.value today 
              , lag(value) over (partition by p.product 
                                     order by p.trx_date) yesterday
              , p.trx_date
          from products p
       ) d
 where trx_date = '2020-06-03'::date ;

使用CTE：
https://www.postgresql.org/docs/12/queries-with.html
举个例子：

CREATE TABLE product_table (product varchar, value integer, trx_date date);
INSERT INTO product_table values ('apple', 100, '06/01/2020'), ('apple', 300, '06/02/2020'), ('apple', 500, '06/03/2020');

WITH prev AS (
    SELECT
        product,
        value
    FROM
        product_table
    WHERE
        trx_date = '06/03/2020'::date - '1 day'::interval
)
SELECT
    pt.product,
    prev.value AS yesterday,
    pt.value AS CURRENT_DATE,
    pt.value - prev.value AS delta
FROM
    product_table AS pt,
    prev
WHERE
    trx_date = '06/03/2020';

 product | yesterday | current_date | delta 
---------+-----------+--------------+-------
 apple   |       300 |          500 |   200