SELECT 
  * 
FROM 
  cscart_lt_vendor_plan_promotions 
WHERE 
  plan_id IN (2, 1, 3, 4)

Query time 0.03511

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_lt_vendor_plan_promotions",
          "access_type": "system",
          "possible_keys": ["PRIMARY"],
          "rows": 1,
          "filtered": 100
        }
      }
    ]
  }
}