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, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    493, 409, 404, 456, 469, 431, 466, 402, 
    439, 484, 470, 490, 451, 491, 411, 486, 
    458, 459, 461, 462, 471, 425, 427, 416, 
    419, 464, 465, 432, 444, 445, 477, 478, 
    487, 488, 434, 435, 515, 481, 489, 415, 
    430, 414, 475, 452, 412, 417, 503, 514
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00061

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "115.21"
    },
    "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": 48,
      "rows_produced_per_join": 48,
      "filtered": "100.00",
      "index_condition": "((`danishecarter_latest`.`cscart_product_descriptions`.`product_id` in (493,409,404,456,469,431,466,402,439,484,470,490,451,491,411,486,458,459,461,462,471,425,427,416,419,464,465,432,444,445,477,478,487,488,434,435,515,481,489,415,430,414,475,452,412,417,503,514)) and (`danishecarter_latest`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "105.61",
        "eval_cost": "9.60",
        "prefix_cost": "115.21",
        "data_read_per_join": "219K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description",
        "unit_name"
      ]
    }
  }
}