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 (
    99492, 99493, 99494, 99495, 99496, 99497, 
    99498, 99499, 99500, 99501, 99502, 
    99503, 99504, 99505, 99506, 99508, 
    99512, 99516, 100399, 100479, 100480, 
    100481, 100484, 100485, 100486, 100501, 
    100502, 100700, 100701, 100702
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00075

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 (99492,99493,99494,99495,99496,99497,99498,99499,99500,99501,99502,99503,99504,99505,99506,99508,99512,99516,100399,100479,100480,100481,100484,100485,100486,100501,100502,100700,100701,100702)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}