sql - 这个 SQL 有效吗？

Question

我对在我的 db_design 中实现连接还很陌生，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(您的查询中缺少该子句)。

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'