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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6b8a8b3ed85dabf1f73d57fc74560f8c8b6d77fd8b1256adb3fc90c9cf4bcdb9' 
  AND token = 'xRLYYONSdWObeDCW9dFcExN4eWEP0MB9Jqhzr+NXA68=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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