postgresql – 我可以使一个plpgsql函数返回一个整数,而不使用一

1)RETURN(SELECT …)

CREATE OR REPLACE FUNCTION get(_param_id integer)
  RETURNS integer AS
$func$
BEGIN

RETURN (SELECT col1 FROM TABLE WHERE id = _param_id);

END
$func$LANGUAGE plpgsql;

2)使用OUT或INOUT参数

CREATE OR REPLACE FUNCTION get(_param_id integer,OUT _col1 integer)
  RETURNS integer AS  -- "RETURNS integer" is optional in this case
$func$
BEGIN

SELECT INTO _col1  col1 FROM TABLE WHERE id = _param_id;

-- also valid,but not as clean:
-- _col1 := col1 FROM TABLE WHERE id = _param_id;

END
$func$LANGUAGE plpgsql;

阅读更多in the manual here.

3)(Ab)使用IN参数

由于PostgreSQL 9.0还可以使用输入参数作为变量.我引用release notes for：

An input parameter now acts like a local variable initialized to the
passed-in value.

人机工程学：

CREATE OR REPLACE FUNCTION get(_param_id integer)
  RETURNS integer AS
$func$
BEGIN

SELECT INTO _param1  col1 FROM TABLE WHERE id = _param1;
RETURN _param1;

-- Also possible,but discouraged:
-- $1 := col1 FROM TABLE WHERE id = $1;
-- RETURN $1;

END
$func$LANGUAGE plpgsql;

最后一个你确实使用一个变量,严格来说,但你不必另外声明.

4)使用带有INOUT参数的DEFAULT值

这是一个特殊情况.

CREATE OR REPLACE FUNCTION get(_param_id integer,INOUT _col1 integer = 123)
  RETURNS integer AS
$func$
BEGIN

-- You can set _col1 to some other value:
-- SELECT INTO _col1  col1 FROM TABLE WHERE id = _param_id;
-- If you don't,123 will be returned.

END
$func$LANGUAGE plpgsql;

5)改用纯SQL function

CREATE OR REPLACE FUNCTION get(_param_id integer)
  RETURNS integer AS
$func$
SELECT col1 FROM TABLE WHERE id = _param_id;  -- use $1 in Postgres 9.1 or older
$func$
  LANGUAGE sql;