SQLITE更新动作

Question

根据SQLite外键文档，它应该是创建两个数据库的方式，并且如果父字段更新，引用父字段的字段也会更新。

问题:一旦我按照下面的步骤，一切都工作正常，直到最后一个命令SELECT * FROM track;，因为结果仍然与以下相同，因此它应该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  

为什么会这样?

Answer 1

你应该更仔细地阅读精细的手册:

2。启用外键支持
[…]
假设库是在启用外键约束的情况下编译的，那么应用程序仍然必须在运行时使用PRAGMA foreign_keys命令启用它。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)，因此必须为每个数据库连接单独启用。

所以如果你这样写:

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

，那么你会在track中看到你所期望的100。当然，这假定您的SQLite是在FK支持下编译的。