Basic transactional DDL script in PostgreSQL

Question

PostgreSQL newbie here trying to put together a transactional DDL script to atomically create a database and its schema in Postgres 9.3: in a transaction, create a few tables; if any errors, roll the whole thing back; otherwise commit. I'm having a hard time getting the syntax right, and I suspect my problems might stem from conflating SQL DDL with PL/pgSQL and/or not grokking the transaction semantics.

Long story short, what's the PL/pgSQL boilerplate for a script to do something like this?

My attempts have gone something like schema.sql here:

BEGIN;

CREATE TABLE IF NOT EXISTS blah ( ... ); -- much DDL

EXCEPTION WHEN OTHERS THEN ROLLBACK; -- this, I gather, is PL/pgSQL

COMMIT;

\i schema.sql at the psql prompt produces a syntax error at or near EXCEPTION. OK, so EXCEPTION must be PL/pgSQL, and all this needs to go in a PL/pgSQL declaration. Let's try again:

Per the grammar at http://www.postgresql.org/docs/9.3/static/plpgsql-structure.html, this looks like:

[ <<label>> ]
[ DECLARE
    declarations ]
BEGIN
    statements
END [ label ];

I don't need to name this, it's a one-off provisioning script, not declaring a function I'm going to use again. So skip the declarations and expand statements to what I had before:

BEGIN

    BEGIN;

    CREATE TABLE IF NOT EXISTS blah ( ... ); -- much DDL

    EXCEPTION WHEN OTHERS THEN ROLLBACK; 

    COMMIT;

END;

This blows up in even worse fashion, with syntax errors on BEGIN, EXCEPTION, and then it keeps running the rest of the script anyways, complaining about not being in a transaction.

What's the misunderstanding I have here?

Answer 1

如果有任何错误，请回滚整个内容；

它比你想象的要简单。事务中的任何异常（未以某种方式捕获）都会自动触发ROLLBACK整个事务的a 。你不需要做任何额外的事情。

BEGIN;
CREATE TABLE IF NOT EXISTS blah ( ... );
-- much more DDL
COMMIT;

你不能启动，提交或回滚事务里面PLPGSQL可言，因为PLPGSQL块总是在外部事务的情况下自动运行。

不要将事务管理的 SQL 命令与plpgsql 代码块的元素混淆。BEGIN两者都用作关键字，这是唯一的共同点。这绝不是模棱两可的，因为 SQL 命令在 plpgsql 代码中不可用，并且在 plpgsql 代码块之外没有 plpgsql 命令。

EXCEPTIONplpgsql 块中的子句仅用于捕获错误并在ROLLBACK. 当然，只有做一些ROLLBACK不会撤销的事情才有意义——比如提出一条永远不会回滚的消息。
您的演示代码不需要任何这些。