在触发器中插入或忽略
我有一个数据库(用于跟踪电子邮件统计信息)已增长到数百兆字节,并且我一直在寻找减少它的方法。
看来文件大小较大的主要原因是相同的字符串往往会在数千行中重复。为了避免这个问题,我计划为字符串池创建另一个表,如下所示:
CREATE TABLE AddressLookup (
ID INTEGER PRIMARY KEY AUTOINCREMENT,
Address TEXT UNIQUE
);
CREATE TABLE EmailInfo (
MessageID INTEGER PRIMARY KEY AUTOINCREMENT,
ToAddrRef INTEGER REFERENCES AddressLookup(ID),
FromAddrRef INTEGER REFERENCES AddressLookup(ID)
/* Additional columns omitted for brevity. */
);
为了方便起见,一个视图来连接这些表:
CREATE VIEW EmailView AS
SELECT
MessageID,
A1.Address AS ToAddr,
A2.Address AS FromAddr
FROM EmailInfo
LEFT JOIN AddressLookup A1 ON (ToAddrRef = A1.ID)
LEFT JOIN AddressLookup A2 ON (FromAddrRef = A2.ID);
为了能够像使用常规表一样使用此视图,我已经做了一些触发器:
CREATE TRIGGER trg_id_EmailView
INSTEAD OF DELETE ON EmailView
BEGIN
DELETE FROM EmailInfo WHERE MessageID = OLD.MessageID;
END;
CREATE TRIGGER trg_ii_EmailView
INSTEAD OF INSERT ON EmailView
BEGIN
INSERT OR IGNORE INTO AddressLookup(Address) VALUES (NEW.ToAddr);
INSERT OR IGNORE INTO AddressLookup(Address) VALUES (NEW.FromAddr);
INSERT INTO EmailInfo
SELECT NEW.MessageID, A1.ID, A2.ID
FROM AddressLookup A1, AddressLookup A2
WHERE A1.Address = NEW.ToAddr AND A2.Address = NEW.FromAddr;
END;
CREATE TRIGGER trg_iu_EmailView
INSTEAD OF UPDATE ON EmailView
BEGIN
UPDATE EmailInfo SET MessageID = NEW.MessageID
WHERE MessageID = OLD.MessageID;
REPLACE INTO EmailView
SELECT NEW.MessageID, NEW.ToAddr, NEW.FromAddr;
END;
问题
之后:
INSERT OR REPLACE INTO EmailView VALUES (1, '[email protected]', '[email protected]');
INSERT OR REPLACE INTO EmailView VALUES (2, '[email protected]', '[email protected]');
更新的行包含:
MessageID ToAddr FromAddr
--------- ------ --------
1 NULL [email protected]
2 [email protected] [email protected]
有一个不应该存在的 NULL。 EmailInfo
表中的相应单元格包含一个孤立的 ToAddrRef
值。
如果您一次执行一个 INSERT,您将看到 AddressLookup
表中的 Alice 的 ID发生了变化!
看来此行为已记录:
ON CONFLICT 子句可以指定为触发器体内 UPDATE 或 INSERT 操作的一部分。但是,如果将 ON CONFLICT 子句指定为导致触发器触发的语句的一部分,则将使用外部语句的冲突处理策略。
因此,顶级“INSERT OR REPLACE”语句中的“REPLACE”将覆盖触发器程序中关键的“INSERT OR IGNORE”。
有什么办法可以让它按照我想要的方式工作吗?
I have a database (for tracking email statistics) that has grown to hundreds of megabytes, and I've been looking for ways to reduce it.
It seems that the main reason for the large file size is that the same strings tend to be repeated in thousands of rows. To avoid this problem, I plan to create another table for a string pool, like so:
CREATE TABLE AddressLookup (
ID INTEGER PRIMARY KEY AUTOINCREMENT,
Address TEXT UNIQUE
);
CREATE TABLE EmailInfo (
MessageID INTEGER PRIMARY KEY AUTOINCREMENT,
ToAddrRef INTEGER REFERENCES AddressLookup(ID),
FromAddrRef INTEGER REFERENCES AddressLookup(ID)
/* Additional columns omitted for brevity. */
);
And for convenience, a view to join these tables:
CREATE VIEW EmailView AS
SELECT
MessageID,
A1.Address AS ToAddr,
A2.Address AS FromAddr
FROM EmailInfo
LEFT JOIN AddressLookup A1 ON (ToAddrRef = A1.ID)
LEFT JOIN AddressLookup A2 ON (FromAddrRef = A2.ID);
In order to be able to use this view as if it were a regular table, I've made some triggers:
CREATE TRIGGER trg_id_EmailView
INSTEAD OF DELETE ON EmailView
BEGIN
DELETE FROM EmailInfo WHERE MessageID = OLD.MessageID;
END;
CREATE TRIGGER trg_ii_EmailView
INSTEAD OF INSERT ON EmailView
BEGIN
INSERT OR IGNORE INTO AddressLookup(Address) VALUES (NEW.ToAddr);
INSERT OR IGNORE INTO AddressLookup(Address) VALUES (NEW.FromAddr);
INSERT INTO EmailInfo
SELECT NEW.MessageID, A1.ID, A2.ID
FROM AddressLookup A1, AddressLookup A2
WHERE A1.Address = NEW.ToAddr AND A2.Address = NEW.FromAddr;
END;
CREATE TRIGGER trg_iu_EmailView
INSTEAD OF UPDATE ON EmailView
BEGIN
UPDATE EmailInfo SET MessageID = NEW.MessageID
WHERE MessageID = OLD.MessageID;
REPLACE INTO EmailView
SELECT NEW.MessageID, NEW.ToAddr, NEW.FromAddr;
END;
The problem
After:
INSERT OR REPLACE INTO EmailView VALUES (1, '[email protected]', '[email protected]');
INSERT OR REPLACE INTO EmailView VALUES (2, '[email protected]', '[email protected]');
The updated rows contain:
MessageID ToAddr FromAddr
--------- ------ --------
1 NULL [email protected]
2 [email protected] [email protected]
There's a NULL that shouldn't be there. The corresponding cell in the EmailInfo
table contains an orphaned ToAddrRef
value.
If you do the INSERTs one at a time, you'll see that Alice's ID in the AddressLookup
table changes!
It appears that this behavior is documented:
An ON CONFLICT clause may be specified as part of an UPDATE or INSERT action within the body of the trigger. However if an ON CONFLICT clause is specified as part of the statement causing the trigger to fire, then conflict handling policy of the outer statement is used instead.
So the "REPLACE" in the top-level "INSERT OR REPLACE" statement is overriding the critical "INSERT OR IGNORE" in the trigger program.
Is there a way I can make it work the way that I wanted?
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好吧,由于 SQLite 是开源的,我只需更改
codeTriggerProgram
函数即可按照应有的方式处理ON CONFLICT
。Well, since SQLite is open-source, I'll just change the
codeTriggerProgram
function to handleON CONFLICT
the way it ought to be.我有/曾经有过类似的问题,我想我找到了一种方法来欺骗 sqlite 正确执行此操作,方法是将
OR REPLACE
从外部语句移动到表本身:当您
INSERT OR REPLACE 时
到表“a”中,您总是替换添加到表 b 中的行,因为触发器现在使用OR REPLACE
。但是,如果您只是执行 INSERT INTO ,它似乎可以工作,因为冲突处理不再是外部插入的一部分,而是表本身的一部分。
I have/had a similar problem and I think I found a way to trick sqlite into doing it right by moving the
OR REPLACE
from the outer statement into the table itself:When you
INSERT OR REPLACE
into table "a" you always replace the row added to table b because the trigger uses theOR REPLACE
now.But if you just do an
INSERT INTO
it seems to work because the on conflict handling is no longer part of the outer insert but part of the table itself.