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 (
    100234, 100235, 100236, 100237, 100238, 
    100239, 100240, 100241, 100242, 100243, 
    100244, 100245, 100246, 100247, 100248, 
    100249, 100250, 100251, 100252, 100253, 
    100254, 100255, 100256, 100257
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00062

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "13.44"
    },
    "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": 24,
      "rows_produced_per_join": 24,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "11.04",
        "eval_cost": "2.40",
        "prefix_cost": "13.44",
        "data_read_per_join": "91K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`nuie_scalesta_net`.`cscart_product_descriptions`.`product_id` in (100234,100235,100236,100237,100238,100239,100240,100241,100242,100243,100244,100245,100246,100247,100248,100249,100250,100251,100252,100253,100254,100255,100256,100257)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}