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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '621b6bf9e5e795302d4876c923bb45318b9dc15019a2a05fd7589b1c4ea2d62c' 
  AND token = 'vNFe/4102lV2MiuW2Y1xvHd0KZM4i+FrfdCd0rmWehI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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