[SQL ]將一個欄位中多項資訊分別放在新欄位問題

[scorsese ()]

大家好，
今天處理一個欄目的資訊分為四個新欄目來處理：
+--------------------------------+
| interests                      |
+--------------------------------+
| women                          |
| sailing, fishing, yachting     |
| fishing, drinking              |
| RPG                            |
| collecting books, scuba diving |
| cooking                        |
| acting, dancing                |
| RPG, anime                     |
| poetry, screenwriting          |
+--------------------------------+
變成：
+------------------+---------------+-----------+-----------+
| interest1        | interest2     | interest3 | interest4 |
+------------------+---------------+-----------+-----------+
| women            |               |           |           |
| sailing          | fishing       | yachting  |           |
| fishing          | drinking      |           |           |
| RPG              |               |           |           |
| collecting books | scuba diving  |           |           |
| cooking          |               |           |           |
| acting           | dancing       |           |           |
| RPG              | anime         |           |           |
| poetry           | screenwriting |           |           |
+------------------+---------------+-----------+-----------+

這段變化我做的指令如下：
ALTER TABLE my_contacts
ADD COLUMN interest1 VARCHAR(50),
ADD COLUMN interest2 VARCHAR(50),
ADD COLUMN interest3 VARCHAR(50),
ADD COLUMN interest4 VARCHAR(50);

UPDATE my_contacts
SET interest1 = SUBSTRING_INDEX(interests, ',', 1);

UPDATE my_contacts
SET interests =
TRIM(RIGHT(interests, (LENGTH(interests)-LENGTH(interest1)-1)));

UPDATE my_contacts
SET interest2 = SUBSTRING_INDEX(interests, ',', 1);

UPDATE my_contacts
SET interests =
TRIM(RIGHT(interests, (LENGTH(interests)-LENGTH(interest2)-1)));

UPDATE my_contacts
SET interest3 = SUBSTRING_INDEX(interests, ',', 1);

UPDATE my_contacts
SET interests =
TRIM(RIGHT(interests, (LENGTH(interests)-LENGTH(interest3)-1)));

UPDATE my_contacts
SET interest4 = interests;

最後再把interests欄位DROP處理掉。

請問這樣處理的結果，空白欄是否應該是NULL?
因為似乎我這樣的處理結果出現的是空白值，而非NULL
且不知道這樣的情形，不是NULL會不會有影響？

先謝謝大家回答！

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→ arkcsl:如果沒有資料，應該是要顯示NULL而不是''
→ arkcsl:如果是我，我會用NULL把全部的''都update掉。
→ arkcsl:因為當你要還原你原本的句子的時候，你會需要用NULL來判斷
→ arkcsl:當然你也可以用length來判斷就是..
→ scorsese:謝謝樓上，我想也是該維持NULL，只是我想怎麼這樣跑的結
→ scorsese:不是NULL呢？
→ arkcsl:set var = NULL where var ='' ?