SQLite中的條件更新

Question

我可以在SQLite中創建類似的語句嗎？

update books set 
(if number_of_pages > 0 then number_of_pages = number_of_pages - 1) 
where book_id = 10 

是否有此工作的語法？

Answer 1

一個CASE語句應使用以下語法工作：

UPDATE 
    books 
SET number_of_page = CASE WHEN number_of_pages > 0 THEN (number_of_pages - 1) ELSE 0 END 
WHERE whatever_condition 

Answer 2

心不是說等於這個說法？

update books set number_of_pages = number_of_pages - 1 where number_of_pages>0 

編輯：

update books set number_of_pages = number_of_pages - 1 where number_of_pages>0 and book_id = 10 

Answer 3

如果你只是想有條件地更新一些行，讓別人完好無損，這應該這樣做：：

update books 
set number_of_pages = number_of_pages - 1 
where number_of_pages > 0 AND book_id = 10 

---

根據新的語句

如果你想更新將所有行（使用book_id = 10）都改爲不同的值，則可以使用2條語句和「相反」條件。假設0是「其他」值，那看起來應該是這樣的：

update books 
set number_of_pages = number_of_pages - 1 
where number_of_pages > 0 AND book_id = 10 

update books 
set number_of_pages = 0 
where number_of_pages <= 0 AND book_id = 10 

或者只是像其他人所建議的那樣使用CASE。