sql - 其他用户能否闯入我的sql操作序列？

Question

我向数据库 (Postgres) 执行插入操作，然后立即获取最后一个序列号。如果 10 个人做同样的事情，他们是否会破坏我的数据库操作顺序？

INSERT INTO table VALUES (DEFAULT,...);
SELECT currval(pg_get_serial_sequence('table','column')) as inserted_id;

恐怕会发生这样的情况:

INSERT INTO table VALUES (DEFAULT,...);
Meanwhile, another user was doing insertions and I end up getting the wrong id;
SELECT currval(pg_get_serial_sequence('table','column')) as inserted_id;

Answer 1

pg_get_serial_sequence(table_name, column_name) 获取 serial、smallserial 或 bigserial 序列的名称列用途。

来自 the PostgreSQL documentation currval 将:

Return the value most recently obtained by nextval for this sequence in the current session. (An error is reported if nextval has never been called for this sequence in this session.) Because this is returning a session-local value, it gives a predictable answer whether or not other sessions have executed nextval since the current session did.

基于以上，注意重点，回答你的问题“如果10个人做同样的事情，他们可以打破我的数据库操作顺序吗？”不是。

这也很容易测试。使用 pgAdmin 的两个实例或您喜欢的任何客户端。

在客户端 1 上:

CREATE TABLE foo (id BIGSERIAL PRIMARY KEY, some_column TEXT);
INSERT INTO foo(some_column) VALUES('a');

在客户端 2 上:

INSERT INTO foo(some_column) VALUES('b');

在客户端 1 上:

SELECT CURRVAL(PG_GET_SERIAL_SEQUENCE('foo','id')) AS inserted_id; -- it will return 1

在客户端 2 上:

SELECT CURRVAL(PG_GET_SERIAL_SEQUENCE('foo','id')) AS inserted_id; -- it will return 2