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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a50a9251c91e5c051547269165197fd18936e3e370dbbd3ad527d9e5a2489c1a' 
  AND token = '8f4IHkBIXeMzEPzZ7qIdQAvsm15mFdSJVLLCaGNhftI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

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