SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    329, 330, 331, 333, 334, 335, 337, 338, 
    339, 341, 342, 343, 371, 372, 373, 374, 
    375, 376, 377, 378
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00063

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "48.01"
    },
    "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": 20,
      "rows_produced_per_join": 20,
      "filtered": "100.00",
      "index_condition": "((`pankajecarter_systemfour`.`cscart_product_descriptions`.`product_id` in (329,330,331,333,334,335,337,338,339,341,342,343,371,372,373,374,375,376,377,378)) and (`pankajecarter_systemfour`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "44.01",
        "eval_cost": "4.00",
        "prefix_cost": "48.01",
        "data_read_per_join": "91K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "unit_name"
      ]
    }
  }
}