max() calculates the maximum across a group of values. For example,

-- Finds the most recent timestamp in the table. 
SELECT max(signed_at) 
FROM blockchains.all_chains

min() calculates the minimum across a group of values. For example,

-- Finds the first timestamp in the table. 
SELECT min(signed_at) 
FROM blockchains.all_chains

To find the corresponding transaction hash (tx_hash) for the max and min signed_at 👇

-- Finds the most recent timestamp in the table.
SELECT max(signed_at), tx_hash
FROM blockchains.all_chains
GROUP BY tx_hash

-- Finds the most recent timestamp in the table.
SELECT min(signed_at), tx_hash
FROM blockchains.all_chains
GROUP BY tx_hash

If you need a non-aggregate function to choose a maximum or minimum of two values, use greatest:

-- Maximum 
SELECT greatest(a, b) FROM table

--Minimum
SELECT least(a, b) FROM table

View all other aggregate functions here