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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b511b0b5eb5b1d49bcf4f444c36f5c6d7db9ed272c83c82c00d9eeefee9a5637' 
  AND token = 'QW8JvLycTGlSXdQQsTn+lLfmPqYYo79Y3WET4+GuFEs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00039

JSON explain

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