SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    379, 378, 377, 376, 375, 374, 373, 372
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00039

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "19.21"
    },
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "product_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "product_id",
        "lang_code"
      ],
      "key_length": "9",
      "rows_examined_per_scan": 8,
      "rows_produced_per_join": 8,
      "filtered": "100.00",
      "index_condition": "((`atulecarter_march_setup`.`cscart_product_descriptions`.`product_id` in (379,378,377,376,375,374,373,372)) and (`atulecarter_march_setup`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "17.61",
        "eval_cost": "1.60",
        "prefix_cost": "19.21",
        "data_read_per_join": "36K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "unit_name"
      ]
    }
  }
}