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 (
    280, 282, 278, 20, 119, 100, 46, 204, 45, 
    68, 29, 6, 8, 14, 9, 10, 19, 21, 7, 27, 124, 
    50, 51, 49, 48, 54, 44, 194, 137, 153, 
    164, 236, 234, 150, 151, 178, 181, 248, 
    65, 64, 63, 62, 66, 140, 141, 144, 143, 
    142, 13
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00078

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "117.61"
    },
    "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": 49,
      "rows_produced_per_join": 49,
      "filtered": "100.00",
      "index_condition": "((`danishecarter_25_march`.`cscart_product_descriptions`.`product_id` in (280,282,278,20,119,100,46,204,45,68,29,6,8,14,9,10,19,21,7,27,124,50,51,49,48,54,44,194,137,153,164,236,234,150,151,178,181,248,65,64,63,62,66,140,141,144,143,142,13)) and (`danishecarter_25_march`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "107.81",
        "eval_cost": "9.80",
        "prefix_cost": "117.61",
        "data_read_per_join": "223K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description",
        "unit_name"
      ]
    }
  }
}