SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.short_description, 
  IF(
    cscart_product_descriptions.short_description = '' 
    OR cscart_product_descriptions.short_description IS NULL, 
    cscart_product_descriptions.full_description, 
    ''
  ) AS full_description, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    1987, 2110, 2111, 2112, 1900, 1813, 1820, 
    2366, 1897, 1750, 1924, 2227, 2204, 
    2010, 2309, 2060, 2122, 2274, 2061, 
    1918, 1913, 1958, 2290, 1751, 1957
  ) 
  AND cscart_product_descriptions.lang_code = 'pl'

Query time 0.00030

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "17.51"
    },
    "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": 25,
      "rows_produced_per_join": 25,
      "filtered": "100.00",
      "index_condition": "((`cscartdevel`.`cscart_product_descriptions`.`product_id` in (1987,2110,2111,2112,1900,1813,1820,2366,1897,1750,1924,2227,2204,2010,2309,2060,2122,2274,2061,1918,1913,1958,2290,1751,1957)) and (`cscartdevel`.`cscart_product_descriptions`.`lang_code` = 'pl'))",
      "cost_info": {
        "read_cost": "15.01",
        "eval_cost": "2.50",
        "prefix_cost": "17.51",
        "data_read_per_join": "133K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description",
        "unit_name"
      ]
    }
  }
}