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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c31abbe05f100c5357a904431260c4d7f972255b536a0379f776ed3523f7fd88' 
  AND token = '9bagbpL3oi+RY7Ckok8vrvMvlaOA2LzuUIi1+lOxVnw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}