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 (
    84651, 84585, 84631, 84621, 84677, 84321, 
    84499, 84565, 84489, 84555, 84545, 
    84611, 84301, 84291, 84667, 84347, 
    84535, 84601, 84546, 84612, 84348, 
    101134, 101135, 101136, 101137, 101138, 
    101139, 101140, 101141, 101142
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00095

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "13.52"
    },
    "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": 30,
      "rows_produced_per_join": 30,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "10.52",
        "eval_cost": "3.00",
        "prefix_cost": "13.52",
        "data_read_per_join": "114K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`nuie_scalesta_net`.`cscart_product_descriptions`.`product_id` in (84651,84585,84631,84621,84677,84321,84499,84565,84489,84555,84545,84611,84301,84291,84667,84347,84535,84601,84546,84612,84348,101134,101135,101136,101137,101138,101139,101140,101141,101142)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}