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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '3f9dbf2ee8f560a5143beff871a857a9b15d44a0b6303a41e50c26be26963f6b' 
  AND token = 'vdg4bdm5iUaDRQv8i1Hg60wL+IwVfoHqSYQVLjHS+Uc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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