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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8276870a47a00acf6fa1830c2950b18d50984b7e03bc11497c2fd8a04a7e4212' 
  AND token = '9dOQ5fvEuUXrEa0qoQzGeNJ2L3lQ/oFvzSqD8rKbzBc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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