Function Postgres创建用于时间戳转换的函数

我试图创建一个postgres函数，它将输入时间戳转换为PDT。这是我的密码：

CREATE OR REPLACE FUNCTION getPdtTimestamp(inTS TIMESTAMP) RETURNS TIMESTAMP AS $$
DECLARE
    outTS TIMESTAMP;
BEGIN
    SELECT TIMESTAMP with time zone inTS AT TIME ZONE 'PDT' INTO outTS;
    RETURN outTS;
END;
$$ LANGUAGE plpgsql;

我在这里得到的错误是：

syntax error at or near "inTS"

我的目标是创建一个查询函数，如下所示：

SELECT TIMESTAMP with time zone '2012-01-01 12:00:00' AT TIME ZONE 'PDT';
// returns a value

提前感谢

这应该可以：

CREATE FUNCTION getPdtTimestamp(timestamp) RETURNS TIMESTAMP AS $$ 
    SELECT $1::TIMESTAMP with time zone  AT TIME ZONE 'PDT';
$$ LANGUAGE SQL;

这应该起作用：

CREATE FUNCTION getPdtTimestamp(timestamp) RETURNS TIMESTAMP AS $$ 
    SELECT $1::TIMESTAMP with time zone  AT TIME ZONE 'PDT';
$$ LANGUAGE SQL;