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 (
    100912, 101107, 101108, 101109, 101116, 
    101117, 101118, 101125, 101126, 101127, 
    101509, 101510, 101511, 101518, 101519, 
    101520, 101527, 101528, 101529, 101547, 
    101548, 101549, 101556, 101557, 101558, 
    101565, 101566, 101567, 101804, 101805, 
    101806, 101807, 101808, 101809, 101810, 
    101811, 101812, 101813
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00090

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "17.12"
    },
    "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": 38,
      "rows_produced_per_join": 38,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "13.32",
        "eval_cost": "3.80",
        "prefix_cost": "17.12",
        "data_read_per_join": "144K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`nuie_scalesta_net`.`cscart_product_descriptions`.`product_id` in (100912,101107,101108,101109,101116,101117,101118,101125,101126,101127,101509,101510,101511,101518,101519,101520,101527,101528,101529,101547,101548,101549,101556,101557,101558,101565,101566,101567,101804,101805,101806,101807,101808,101809,101810,101811,101812,101813)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}