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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '688a82d29e41b435b11579e8ea2593885d560da0b9e13b5f9c6d74c6c069972b' 
  AND token = '3rNh6V5INEVD//sPxa3hRWvbEkff4vdHTidva/xIr9w=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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