PostgreSQL IF-THEN-ELSE控制结构

Why do I always get the following error from Postgres?

为什么我总是从Postgres得到以下错误？

syntax error at or near "IF"

“IF”处或附近的语法错误

I read PostgreSQL: Documentation: 8.3: Control Structures. First I tried to execute a difficult query (with subquery), but then I tried to execute a simple one like this:

我读了PostgreSQL：文档：8.3：控制结构。首先，我尝试执行一个困难的查询（使用子查询），但后来我尝试执行这样一个简单的查询：

IF 2 <> 0 THEN select * from users; END IF;

The error is still the same. What am I doing wrong?

错误仍然相同。我究竟做错了什么？

3 个解决方案

#1

IF 2 <> 0 THEN select * from users; END IF;

You cannot use PL/pgSQL statements outside plpgsql functions. And if this fragment is from plpgsql function, then it is nonsense too. You cannot directly return result of query like T-SQL does.

您不能在plpgsql函数之外使用PL / pgSQL语句。如果这个片段来自plpgsql函数，那么它也是无意义的。你不能像T-SQL那样直接返回查询结果。

CREATE OR REPLACE FUNCTION test(p int)
RETURNS SETOF users AS $$
BEGIN
  IF p = 1 THEN
    RETURN QUERY SELECT * FROM users;
  END IF;
  RETURN;
END;
$$ LANGUAGE plpgsql;

When you would get some result from function, you have to use RETURN statement - plpgsql knows only function, it doesn't support procedures - so unbounded SELECT has not sense.

当你从函数得到一些结果时，你必须使用RETURN语句 - plpgsql只知道函数，它不支持程序 - 所以无限制的SELECT没有意义。

#2

You're not enclosing that PL/pgSQL control structure in an anonymous block or a PL/pgSQL function.

您没有将该PL / pgSQL控件结构包含在匿名块或PL / pgSQL函数中。

For the SQL version of this control structure see the docs for CASE.

对于此控件结构的SQL版本，请参阅CASE的文档。

#3

You're not enclosing that PL/pgSQL. They need to be enclosed with anonymous code block. Example for your code:

你没有附上那个PL / pgSQL。它们需要包含匿名代码块。代码示例：

DO $$ BEGIN

    IF 2 <> 0 THEN select * from users; END IF;

END$$;

#1

IF 2 <> 0 THEN select * from users; END IF;