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 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    282971, 286602, 283081, 283125, 286561, 
    282507, 283098, 279396, 286611, 282889, 
    282945, 286621, 277944, 286500, 286533, 
    284472, 286574, 279355, 278025, 278209, 
    285797, 279438, 270384, 281368, 270320, 
    286493, 277872, 286557, 278250, 278190, 
    285798, 285799, 285796, 285794, 286704, 
    281369
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00281

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "50.47"
    },
    "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": 36,
      "rows_produced_per_join": 36,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "43.27",
        "eval_cost": "7.20",
        "prefix_cost": "50.47",
        "data_read_per_join": "245K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`webmarco`.`cscart_product_descriptions`.`product_id` in (282971,286602,283081,283125,286561,282507,283098,279396,286611,282889,282945,286621,277944,286500,286533,284472,286574,279355,278025,278209,285797,279438,270384,281368,270320,286493,277872,286557,278250,278190,285798,285799,285796,285794,286704,281369)) and (`webmarco`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}