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 (
    453, 454, 455, 450, 451, 452, 435, 439, 
    443, 430, 429, 428, 415, 416, 417, 418, 
    419, 420, 421, 422, 423, 424, 425, 426, 
    403, 404, 405, 406, 407, 408, 409, 410, 
    411, 412, 413, 414, 391, 392, 393, 394, 
    395, 396, 397, 398, 399, 400, 401, 402, 
    379, 380, 381, 382, 383, 384, 385, 386, 
    387, 388, 389, 390, 363, 364, 365, 366
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00093

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "153.61"
    },
    "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": 64,
      "rows_produced_per_join": 64,
      "filtered": "100.00",
      "index_condition": "((`pankajecarter_systemfour`.`cscart_product_descriptions`.`product_id` in (453,454,455,450,451,452,435,439,443,430,429,428,415,416,417,418,419,420,421,422,423,424,425,426,403,404,405,406,407,408,409,410,411,412,413,414,391,392,393,394,395,396,397,398,399,400,401,402,379,380,381,382,383,384,385,386,387,388,389,390,363,364,365,366)) and (`pankajecarter_systemfour`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "140.81",
        "eval_cost": "12.80",
        "prefix_cost": "153.61",
        "data_read_per_join": "292K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description",
        "unit_name"
      ]
    }
  }
}