Question

第一个查询涉及与特定主题相关的书籍和作者的列表，并产生正确的结果：

SELECT BOOK_NUM,
BOOK_TITLE,
BOOK_SUBJECT,
AU_LNAME
FROM BOOK
JOIN WRITES USING (BOOK_NUM)
JOIN AUTHOR USING (AU_ID)
WHERE BOOK_SUBJECT = 'CLOUD'
ORDER BY BOOK_TITLE;

第二个扩展了主题，并产生了正确的结果：

SELECT BOOK_NUM,
BOOK_TITLE,
BOOK_SUBJECT,
AU_FNAME,
AU_LNAME,
Count(BOOK_TITLE) AS `NUM BOOKS BY AUTHOR`
FROM BOOK
JOIN WRITES USING (BOOK_NUM)
JOIN AUTHOR USING (AU_ID)
GROUP BY BOOK_NUM, AU_ID
ORDER BY `NUM BOOKS BY AUTHOR`,
AU_LNAME;

当我将两者结合时，会在WHERE BOOK_SUBJECT ='CLOUD'处产生语法错误：

SELECT BOOK_NUM,
BOOK_TITLE,
BOOK_SUBJECT,
AU_FNAME,
AU_LNAME,
Count(BOOK_TITLE) AS `NUM BOOKS BY AUTHOR`
FROM BOOK
JOIN WRITES USING (BOOK_NUM)
JOIN AUTHOR USING (AU_ID)
GROUP BY BOOK_NUM, AU_ID
WHERE BOOK_SUBJECT = 'CLOUD'
ORDER BY `NUM BOOKS BY AUTHOR`, 
AU_LNAME,
BOOK_TITLE;

无论放置在哪里，都会出现相同的错误，如果将其删除，代码将运行。我需要做什么来解决这个问题？我需要将此where子句包括在内。预先感谢您对我的帮助。

Answer 1

不确定所使用的SQL。尝试将WHERE子句移到GROUP BY上方。

Answer 2

好问题。尝试参考一些有关表达式顺序的文档...

请尝试以下代码，在其中适当地移动了WHERE语句。

SELECT 
BOOK_NUM,
BOOK_TITLE,
BOOK_SUBJECT,
AU_FNAME,
AU_LNAME,
Count(BOOK_TITLE) AS `NUM BOOKS BY AUTHOR`

FROM BOOK
JOIN WRITES USING (BOOK_NUM)
JOIN AUTHOR USING (AU_ID)

WHERE BOOK_SUBJECT = 'CLOUD'

GROUP BY BOOK_NUM, AU_ID

ORDER BY `NUM BOOKS BY AUTHOR`, 
AU_LNAME,
BOOK_TITLE;

2个查询分别工作良好，但结合使用会产生语法错误

2 个答案: