SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.product, 
  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 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    4341, 4342, 6036, 4347, 6369, 4344, 4345, 
    5303, 6050, 7351, 5304, 4348, 4346, 
    6349, 6345, 4122, 2743, 3544, 3545, 
    3543, 3541, 3540, 4956, 5114, 2645, 
    7301, 7299, 7300, 2646, 2647, 2644, 
    1410, 5154, 5150, 5153, 2648, 5152, 
    5155, 5151, 2886, 6436, 2773, 6440, 
    7223, 7116, 7221, 7222, 7224
  ) 
  AND cscart_product_descriptions.lang_code = 'de'

Query time 0.00098

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "33.61"
    },
    "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": 48,
      "rows_produced_per_join": 48,
      "filtered": "100.00",
      "index_condition": "((`dbggbern`.`cscart_product_descriptions`.`product_id` in (4341,4342,6036,4347,6369,4344,4345,5303,6050,7351,5304,4348,4346,6349,6345,4122,2743,3544,3545,3543,3541,3540,4956,5114,2645,7301,7299,7300,2646,2647,2644,1410,5154,5150,5153,2648,5152,5155,5151,2886,6436,2773,6440,7223,7116,7221,7222,7224)) and (`dbggbern`.`cscart_product_descriptions`.`lang_code` = 'de'))",
      "cost_info": {
        "read_cost": "28.81",
        "eval_cost": "4.80",
        "prefix_cost": "33.61",
        "data_read_per_join": "183K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "product",
        "short_description",
        "full_description"
      ]
    }
  }
}