Demonstrate how to do incremental load

incremental_load.sql

-- Not Recommended Approach: Scan the entire table and rebuild everyday
INSERT OVERWRITE TABLE dim_total_bookings PARTITION (ds = '{{ ds }}')
SELECT
     dim_market
  ,  SUM(m_bookings) AS m_bookings
FROM
  fct_bookings
WHERE
  ds <= '{{ ds }}' -- this is expensive, and can quickly run into scale issue
GROUP BY
  dim_market
;

-- Recommended Approach: Incremental Load
INSERT OVERWRITE TABLE dim_total_bookings PARTITION (ds = '{{ ds }}')
SELECT
    dim_market
  , SUM(m_bookings) AS m_bookings
FROM (
  SELECT
      dim_market
    , m_bookings
  FROM
    dim_total_bookings            -- a dim table
  WHERE
    ds = DATE_SUB('{{ ds }}', 1)  -- from the previous ds

  UNION
  
  SELECT
      dim_market
    , SUM(m_bookings) AS m_bookings
  FROM
    fct_bookings                  -- a fct table
  WHERE
    ds = '{{ ds }}'               -- from the current ds
  GROUP BY
     dim_market
) a
GROUP BY
  dim_market
;

Hello,
Can you explain what is ds here and also can you share your datasets