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 (
    39503, 40547, 40112, 40580, 40714, 40836, 
    40232, 40208, 40469, 40616, 40738, 
    40088, 40374, 40787, 40679, 40516, 
    40350, 40812, 40762, 40160, 40326, 
    40422, 40136, 40302, 39585, 40901, 
    40896, 40861, 40865, 40893, 40874, 
    40862, 40873, 40877, 40884, 40887, 
    40891, 40892, 40890, 40883, 40889, 
    40869, 40864, 40880, 40870, 40871, 
    40872, 40875, 40876, 40867, 40879, 
    40886, 40866, 40885, 40888
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00138

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "95.90"
    },
    "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": 55,
      "rows_produced_per_join": 55,
      "filtered": "100.00",
      "index_condition": "((`cscartdb`.`cscart_product_descriptions`.`product_id` in (39503,40547,40112,40580,40714,40836,40232,40208,40469,40616,40738,40088,40374,40787,40679,40516,40350,40812,40762,40160,40326,40422,40136,40302,39585,40901,40896,40861,40865,40893,40874,40862,40873,40877,40884,40887,40891,40892,40890,40883,40889,40869,40864,40880,40870,40871,40872,40875,40876,40867,40879,40886,40866,40885,40888)) and (`cscartdb`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "90.40",
        "eval_cost": "5.50",
        "prefix_cost": "95.90",
        "data_read_per_join": "210K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ]
    }
  }
}