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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51d8086f62ce210fa8d46c06c16291217d409f6949b21c0e05fd57d43d240cd1' 
  AND token = 'RMV1AHsCN1UB26B+34oz8WP6nM40FCIyIO6JlckqtTQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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