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 (
    66798, 66799, 66800, 66801, 66802, 66803, 
    66804, 66805, 66806, 66807, 66808, 
    66809, 66810, 66811, 66812, 66813, 
    66814, 66815, 66816, 66817, 66818, 
    66819, 66820, 66821, 66822, 66823, 
    66824, 66825, 66826, 66827, 66828, 
    66904, 66905
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00075

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "25.59"
    },
    "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": 33,
      "rows_produced_per_join": 33,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "22.29",
        "eval_cost": "3.30",
        "prefix_cost": "25.59",
        "data_read_per_join": "150K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`cscart_db`.`cscart_product_descriptions`.`product_id` in (66798,66799,66800,66801,66802,66803,66804,66805,66806,66807,66808,66809,66810,66811,66812,66813,66814,66815,66816,66817,66818,66819,66820,66821,66822,66823,66824,66825,66826,66827,66828,66904,66905)) and (`cscart_db`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}