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 (
    100682, 100683, 100684, 100685, 100686, 
    100687, 100688, 100689, 100690, 100691, 
    100692, 100693, 100694, 100695, 101011, 
    101012, 101013, 101014, 101015, 101016, 
    101017, 101018, 101019, 101020, 101021, 
    101625, 101684, 101685, 101686, 101687, 
    101694, 101695, 101963
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00066

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "14.87"
    },
    "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": "11.57",
        "eval_cost": "3.30",
        "prefix_cost": "14.87",
        "data_read_per_join": "125K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`nuie_scalesta_net`.`cscart_product_descriptions`.`product_id` in (100682,100683,100684,100685,100686,100687,100688,100689,100690,100691,100692,100693,100694,100695,101011,101012,101013,101014,101015,101016,101017,101018,101019,101020,101021,101625,101684,101685,101686,101687,101694,101695,101963)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}