92语法添加一个外键到你的表中，如下所示：

pre $ alter table child ADD CONSTRAINT fk_child_parent
FOREIGN KEY（parent_id）
REFERENCES parent（id）;


SQLite不支持 ADD CONSTRAINT $ c> ALTER TABLE 命令的变体（ sqlite.org：SQLite没有实现的SQL特性）。因此，在sqlite 3.6.1中添加外键的唯一方法是在 CREATE TABLE 过程中，如下所示：





  CREATE TABLE child（
 id INTEGER PRIMARY KEY，
 parent_id INTEGER，
 description TEXT ，
 FOREIGN KEY（parent_id）REFERENCES parent（id）
）; 
 

不幸的是，您必须将现有数据保存到临时表中，删除旧表，创建新的FK约束表，然后将数据从临时表中复制回来。 （ sqlite.org - FAQ：Q11 ）

I have the following table:

CREATE TABLE child( 
  id INTEGER PRIMARY KEY, 
  parent_id INTEGER, 
  description TEXT);

How do I add a foreign key constraint on parent_id? Assume foreign keys are enabled.

Most examples assume you're creating the table - I'd like to add the constraint to an existing one.

You can't.

Although the SQL-92 syntax to add a foreign key to your table would be as follows:

ALTER TABLE child ADD CONSTRAINT fk_child_parent
                  FOREIGN KEY (parent_id) 
                  REFERENCES parent(id);

SQLite doesn't support the ADD CONSTRAINT variant of the ALTER TABLE command (sqlite.org: SQL Features That SQLite Does Not Implement).

Therefore, the only way to add a foreign key in sqlite 3.6.1 is during CREATE TABLE as follows:

CREATE TABLE child ( 
    id           INTEGER PRIMARY KEY, 
    parent_id    INTEGER, 
    description  TEXT,
    FOREIGN KEY (parent_id) REFERENCES parent(id)
);

Unfortunately you will have to save the existing data to a temporary table, drop the old table, create the new table with the FK constraint, then copy the data back in from the temporary table. (sqlite.org - FAQ: Q11)