(SELECT

block_number as block,

block_timestamp,

'ethereum' as title,

lag(block_timestamp, 1) OVER (ORDER BY block_number) as ptime

from ethereum.core.fact_blocks

WHERE block_timestamp BETWEEN CURRENT_DATE-20 AND CURRENT_DATE-2)

select AVG(TIMEDIFF(milliseconds, ptime, block_timestamp)) as block_time from polygon