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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c475ce70b7e8d8acada9d47139f44eb0127e05ad865d26e8d2fb48509436d618' 
  AND token = 'sKlfvRRce0ikCyamtGDS77+oCde0esG/h7byRbEdqUM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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