sql - SQLITE更新操作

Question

基于SQLite foreign key documentation，它应该是创建两个数据库的方式，并且如果父字段被更新，则引用父字段的字段也将被更新。

问题：执行以下步骤后，一切正常，直到最后一条命令为止
SELECT * FROM track;因为结果仍然保持不变，因此应更改为最后显示的结果。

  trackid  trackname          trackartist
    -------  -----------------  -----------
    11       That's Amore       1
    12       Christmas Blues    1
    13       My Way             2  

编码：

-- Database schema
CREATE TABLE artist(
  artistid    INTEGER PRIMARY KEY, 
  artistname  TEXT
);
CREATE TABLE track(
  trackid     INTEGER,
  trackname   TEXT, 
  trackartist INTEGER REFERENCES artist(artistid) ON UPDATE CASCADE
);

sqlite> SELECT * FROM artist;
artistid  artistname       
--------  -----------------
1         Dean Martin      
2         Frank Sinatra    

sqlite> SELECT * FROM track;
trackid  trackname          trackartist
-------  -----------------  -----------
11       That's Amore       1
12       Christmas Blues    1
13       My Way             2  

sqlite> -- Update the artistid column of the artist record for "Dean Martin".
sqlite> -- Normally, this would raise a constraint, as it would orphan the two
sqlite> -- dependent records in the track table. However, the ON UPDATE CASCADE clause
sqlite> -- attached to the foreign key definition causes the update to "cascade"
sqlite> -- to the child table, preventing the foreign key constraint violation.
sqlite> UPDATE artist SET artistid = 100 WHERE artistname = 'Dean Martin';

sqlite> SELECT * FROM artist;
artistid  artistname       
--------  -----------------
2         Frank Sinatra    
100       Dean Martin      

sqlite> SELECT * FROM track;
trackid  trackname          trackartist
-------  -----------------  -----------
11       That's Amore       100
12       Christmas Blues    100  
13       My Way             2  

为什么是这样？

Answer 1

您应该更仔细地阅读fine manual：


2.启用外键支持
[...]
假设在编译库时启用了外键约束，则应用程序仍必须在运行时使用PRAGMA foreign_keys命令启用该库。例如：

sqlite> PRAGMA foreign_keys = ON;

默认情况下，外键约束是禁用的（为了向后兼容），因此必须分别为每个数据库连接分别启用。


因此，如果您这样说：

sqlite> PRAGMA foreign_keys = ON;
sqlite> UPDATE artist SET artistid = 100 WHERE artistname = 'Dean Martin';

那么您会在期望的 track中看到100。当然，这假定您的SQLite是在FK支持下编译的。