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 (
    1674, 1642, 1672, 2185, 1629, 1659, 1637, 
    1667, 1645, 1676, 2159, 1653, 1684, 
    1631, 1661, 2216, 2218, 2229, 2228, 
    1639, 1669, 1628, 1658, 1633, 1663
  ) 
  AND cscart_product_descriptions.lang_code = 'pl'

Query time 0.00044

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 (1674,1642,1672,2185,1629,1659,1637,1667,1645,1676,2159,1653,1684,1631,1661,2216,2218,2229,2228,1639,1669,1628,1658,1633,1663)) 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"
      ]
    }
  }
}