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 (
    1634, 1664, 1641, 1671, 1627, 1657, 1655, 
    1686, 1646, 1677, 1636, 1666, 1638, 
    1668, 1644, 1674, 1642, 1672, 2185, 
    1629
  ) 
  AND cscart_product_descriptions.lang_code = 'pl'

Query time 0.00038

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "14.01"
    },
    "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": "((`cscartdevel`.`cscart_product_descriptions`.`product_id` in (1634,1664,1641,1671,1627,1657,1655,1686,1646,1677,1636,1666,1638,1668,1644,1674,1642,1672,2185,1629)) and (`cscartdevel`.`cscart_product_descriptions`.`lang_code` = 'pl'))",
      "cost_info": {
        "read_cost": "12.01",
        "eval_cost": "2.00",
        "prefix_cost": "14.01",
        "data_read_per_join": "106K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description",
        "unit_name"
      ]
    }
  }
}