Sqlite sqlalchemy外键仅适用于主键？

表和外键正在创建正常，但工作不正常：

SQLite version 3.7.9 2011-11-01 00:52:41
sqlite> pragma foreign_keys=on;
sqlite> 
sqlite> CREATE TABLE t1(id int primary key, uuid varchar(36));
sqlite> CREATE TABLE t2(id int primary key, t1_uuid varchar(36), FOREIGN KEY (t1_uuid)    REFERENCES t1(uuid));
sqlite> 
sqlite> INSERT INTO t1(uuid) values ("uuid-1");
sqlite> INSERT INTO t2(t1_uuid) values ("uuid-1");
Error: foreign key mismatch

但是，如果我使用t1（uuid）主键，所有功能都会按预期工作：

sqlite> pragma foreign_keys=off;
sqlite> DROP TABLE t1;
sqlite> DROP TABLE t2;
sqlite> pragma foreign_keys=on;
sqlite> CREATE TABLE t1(id int, uuid varchar(36) primary key);
sqlite> CREATE TABLE t2(id int primary key, t1_uuid varchar(36), FOREIGN KEY (t1_uuid) REFERENCES t1(uuid));
sqlite> INSERT INTO t1(uuid) values ("uuid-1");
sqlite> INSERT INTO t2(t1_uuid) values ("uuid-1");

创建索引时不做任何操作：

sqlite> pragma foreign_keys=on;
sqlite> CREATE TABLE t1(id int primary key, uuid varchar(36));
sqlite> CREATE INDEX uuindex ON t1(uuid);
sqlite> CREATE TABLE t2(id int primary key, t1_uuid varchar(36), FOREIGN KEY (t1_uuid) REFERENCES t1(uuid));
sqlite> INSERT INTO t1(uuid) values ("uuid-1");
sqlite> INSERT INTO t2(t1_uuid) values ("uuid-1");
Error: foreign key mismatch

报告说：

通常，外键约束的父键是父表的主键。如果它们不是主键，则父键列必须共同受唯一约束或具有唯一索引