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 (
    100187, 100188, 100189, 100190, 100191, 
    100192, 100193, 100194, 100195, 100196, 
    100197, 100198, 100199, 100200, 100201, 
    100202, 100203, 100204, 100205, 100206, 
    100207, 100208, 100209, 100210, 100211, 
    100217, 100218, 100219, 100220, 100221
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00069

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 (100187,100188,100189,100190,100191,100192,100193,100194,100195,100196,100197,100198,100199,100200,100201,100202,100203,100204,100205,100206,100207,100208,100209,100210,100211,100217,100218,100219,100220,100221)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}