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 (
    51603, 119291, 243684, 275040, 275133, 
    275759, 275765, 276261, 276352, 276420, 
    276421, 276426, 276427, 276428, 276429, 
    276430, 276431, 276432, 276433, 276434, 
    276435, 276436, 276437, 276438, 276439, 
    276440, 276441, 276442, 276443, 276444
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00104

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "66.01"
    },
    "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",
      "index_condition": "((`s2cart`.`cscart_product_descriptions`.`product_id` in (51603,119291,243684,275040,275133,275759,275765,276261,276352,276420,276421,276426,276427,276428,276429,276430,276431,276432,276433,276434,276435,276436,276437,276438,276439,276440,276441,276442,276443,276444)) and (`s2cart`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "63.01",
        "eval_cost": "3.00",
        "prefix_cost": "66.01",
        "data_read_per_join": "227K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ]
    }
  }
}