MySQL的 - 不能根據「ques_id」列

Question

SELECT ques_id,ans_desc 
FROM answer 
ORDER BY ans_desc 
HAVING ans_desc=0 

Answer 1

使用ans_desc IS NULL謂詞WHERE子句中的「ans_desc」一欄得到NULL值：

SELECT ques_id, ans_desc 
FROM answer 
WHERE ans_desc = 0 OR ans_desc IS NULL 
ORDER BY ans_desc ; 

這將只有那些給你ans_desc列中的0或NULL值。

僅WHERE ans_desc = 0將不會給出NULL值。

Answer 2

0是NULL並且不同於空

SELECT ques_id,ans_desc 
FROM answer 
WHERE ISNULL(ans_desc) OR ans_desc = '' 
ORDER BY ans_desc 

Answer 3

我不認爲你甚至需要「通過ans_desc秩序」，當你需要選擇只與NULL值的行。

你應該這樣做：

SELECT ques_id as `question`, ans_desc as `answer` 
FROM answer 
WHERE ans_desc is NULL; 

此查詢的優點是，它不使用文件排序。

請參閱您正在使用瞭解更多的查詢的解釋輸出。

希望有所幫助。