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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6db24dfbc9621e2e7f17273b5b0e667baae7fc592e0bafb1812a1487834494db' 
  AND token = 'sMx5o9A69VqLaBA4Sae4IvANkByywosxifLLcv6C02E=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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