我有这个
MySQL的片段:
CREATE TABLE seq_test (
id INT PRIMARY KEY AUTO_INCREMENT,
name TEXT
);
INSERT INTO seq_test(id, name) VALUES (1, 'one');
INSERT INTO seq_test(name) VALUES ('two');
当我尝试在PostgreSQL中编写它时:
CREATE TABLE seq_test (
id SERIAL PRIMARY KEY,
name TEXT
);
INSERT INTO seq_test(id, name) VALUES (1, 'one');
INSERT INTO seq_test(name) VALUES ('two');
我收到以下错误:
[23505] ERROR: duplicate key value violates unique constraint "seq_test_pkey"
Detail: Key (id)=(1) already exists.
这是因为在PostgreSQL中,插入一个不会增加下一个插入的id.如何创建表以使其符合MySQL行为?
这是一个人为的例子,但是我将一个从MySQL迁移到PostgreSQL的大型代码库,部分代码(我无法控制)使用两种样式(即有和没有id),它们在MySQL中工作但是在PostgreSQL中不起作用.
一个丑陋的黑客就是总是做SELECT setval(‘my_table_id_seq’,(SELECT count(*)FROM my_table),TRUE)……
最佳答案 对此没有任何不解决的解决方案:您要么坚持SERIAL功能,要么自己处理.
但是你让我感兴趣,而且我已经想出了这个(我希望有点少hacky)解决方案:创建一个触发器来完成所有肮脏的工作.
触发功能
(添加通知,以便我们可以看到发生了什么):
CREATE OR REPLACE FUNCTION update_seq_val_seq_test()
RETURNS TRIGGER AS $$
BEGIN
RAISE NOTICE 'id is %', NEW.id;
IF NEW.id > currval('seq_test_id_seq' :: REGCLASS)
THEN
RAISE NOTICE 'curval is %', currval('seq_test_id_seq' :: REGCLASS);
PERFORM setval('seq_test_id_seq' :: REGCLASS, (NEW.id) :: BIGINT);
RAISE NOTICE 'new curval is %', currval('seq_test_id_seq' :: REGCLASS); END IF;
RETURN NULL;
END;
$$
LANGUAGE 'plpgsql' COST 1;
设置触发器
CREATE TRIGGER seq_test_update_serial
AFTER INSERT ON seq_test
FOR EACH ROW EXECUTE PROCEDURE update_seq_val_seq_test();
拉动扳机
Fast’n’dirty测试
tests2=# insert into seq_test (name) values ('first');
NOTICE: id is 30
INSERT 0 1
tests2=# select * from seq_test;
id | name
----+-------
30 | first
(1 row)
tests2=# select currval('seq_test_id_seq'::regclass);
currval
---------
30
(1 row)
tests2=# insert into seq_test (id, name) values (31, 'thirty one');
NOTICE: id is 31
NOTICE: curval is 30
NOTICE: new curval is 31
INSERT 0 1
tests2=# select currval('seq_test_id_seq'::regclass);
currval
---------
31
(1 row)
tests2=# select * from seq_test;
id | name
----+------------
30 | first
31 | thirty one
(2 rows)
tests2=# insert into seq_test (name) values ('thirty dunno what');
NOTICE: id is 32
INSERT 0 1
tests2=# insert into seq_test (id, name) values (21, 'back to the future');
NOTICE: id is 21
INSERT 0 1
tests2=# select currval('seq_test_id_seq'::regclass);
currval
---------
32
(1 row)
tests2=# select * from seq_test;
id | name
----+--------------------
30 | first
31 | thirty one
32 | thirty dunno what
21 | back to the future
(4 rows)
tests2=# insert into seq_test (name) values ('thirty dunno what++');
NOTICE: id is 33
INSERT 0 1
tests2=# select * from seq_test;
id | name
----+---------------------
30 | first
31 | thirty one
32 | thirty dunno what
21 | back to the future
33 | thirty dunno what++
(5 rows)
所以,现在Postgres正在处理这个案例,就像你想要的那样,但是有很多东西要检查你:如何使用批量插入,回滚,这个触发器如何影响性能,以及更多的乐趣.