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Foreign Key constraint doesn't work（1个答案）
昨天关门了。

• python版本：3.8.10
• sqlite3.version：2.6.0
• sqlite3.sqlite_version：3.31.1

我有两张table：blocklist和blocklist_reasons。请参见以下内容：

blocklist_reasons
id | reason
--------------------------
1  | Source not supported

blocklist
id | link            | reason
-----------------------------
1  | https://mega.nz | 1

blocklist.reason引用blocklist_reasons.id，因此设置了外键约束。
但是，我可以插入任何我想要的数字，它仍然会接受，这很奇怪：

sqlite> INSERT INTO blocklist(link, reason) VALUES ('https://example.com', 2);
sqlite> -- No problems eventhough there is no row in blocklist_reasons with ID 2???
sqlite> SELECT * FROM blocklist;
1|https://mega.nz|1
2|https://example.com|2

我可以用下面的代码重现这个问题：

-- Create reasons table and add one reason with ID 1
CREATE TABLE blocklist_reasons(
    id INTEGER PRIMARY KEY,
    reason TEXT NOT NULL UNIQUE
);
INSERT INTO blocklist_reasons(reason) VALUES ('Source not supported');
SELECT * FROM blocklist_reasons;
1|Source not supported

-- Create blocklist table and insert row with reason ID set as ID 2 without errors
CREATE TABLE blocklist(
    id INTEGER PRIMARY KEY,
    link TEXT NOT NULL,
    reason INTEGER NOT NULL,
    FOREIGN KEY (reason) REFERENCES blocklist_reasons(id)
);
INSERT INTO blocklist(link, reason) VALUES ('https://mega.nz', 2);
SELECT * FROM blocklist;
1|https://mega.nz|2

您可以看到，我插入了reason列设置为2的行，即使blocklist_reasons表中没有ID为2的行，也能正常工作。为什么外键约束没有引发错误？