Query for all chains if no chain parameter present

[0237h]

Previously when not passing any chain parameter with the query, the result would be the first row in the DB matching the expression. This change now runs the query as a UNION between all the available chains in the DB when no chain parameter is passed.

Example

SELECT *FROM blocks
WHERE (CHAIN == 'testnet') ORDER BY block_number DESC LIMIT 2 
UNION ALL 
SELECT * FROM blocks 
WHERE (chain == 'polygon') ORDER BY block_number DESC LIMIT 2 
UNION ALL 
SELECT * FROM blocks 
WHERE (chain == 'mainnet') ORDER BY block_number DESC LIMIT 2