这个SQL有效吗？

Question

我仍然是在我的db_design中实现连接的新手,我不确定这个SQL是否有效.

"SELECT * FROM notes JOIN small_note ON notes_id = '$id' AND authname = '$author' AND bookname = '$book' AND user = '$username'"

这样更容易阅读:

"SELECT * FROM notes
    JOIN small_note ON notes_id = '$id'
    AND authname = '$author'
    AND bookname = '$book'
    AND user = '$username'";

Answer 1

不,不是.

您需要为两个表指定连接列,并且需要确保使用正确的WHERE子句(查询中缺少该子句).

这可能更合适:

SELECT * FROM notes n
JOIN small_note  sn
  ON n.notes_id = sn.notes_id
WHERE notes_id = '$id' 
  AND authname = '$author' 
  AND bookname = '$book' 
  AND user = '$username'