以日期为参数的函数，可以为 NULL

Question

我正在尝试在 PostgreSQL 9.3.5 中实现一个以日期为参数的函数。
它应该涵盖以下所有条件并相应地返回结果。

select * from tablename
where sid is not null and dob >= '11-14-2014' order by dob;
-- Only Start Date

select * from tablename
where sid is not null and dob <= '11-21-2014' order by dob;
-- Only End Date

select * from tablename
where sid is not null and dob between '11-10-2014' and '11-21-2014' order by dob; 
-- Both Start and End Dates are Given

select * from tablename
where sid is not null and dob is null; 
-- Both Start and End Dates are Null

SQL Fiddle

但是我上面的 SQL Fiddle 没有按预期工作。

我想要一个通用的实现，这样如果明天我有更多的new Date Fields 到条件搜索中，那么我可以将它们添加到where condition 中，但不能添加到IF 语句的每一行中。

Updated SQL Fiddle

Answer 1

这可以简单得多：

您可以将@Clodoaldo 目前接受的答案中的表达式简化为：

SELECT *
FROM   sampletest
WHERE  eid IS NOT NULL
AND   (_sd IS NULL AND _ed IS NULL OR
       _sd IS NULL AND dob <= _ed  OR
       _ed IS NULL AND dob >= _sd  OR
       dob BETWEEN _sd AND _ed);

• 比较dob >= _sd后，无需另外检查_sd is not null。
  无论如何，表达式只能计算为 TRUE 和非空 _sd。

但这些都不是必需的：

CREATE OR REPLACE FUNCTION test_dob_dates(_sd date, _ed date)
  RETURNS SETOF sampletest AS
$func$
SELECT *
FROM   sampletest
WHERE  eid IS NOT NULL
AND    dob BETWEEN COALESCE(_sd, -infinity) AND COALESCE(_ed, infinity)
$func$ LANGUAGE sql STABLE;

• 不要引用语言名称。这是一个标识符。
• Postgres 为timestamp 和date 类型提供special values -infinity and infinity。您只需使用COALESCE 将这些值默认为这些值。

SQL Fiddle（适用于第 9.3 页）。

除此之外：我建议使用标准 ISO 日期 '2014-11-10' 而不是 '11-10-2014'，这可能会模棱两可并且会因不同的区域设置而中断。 The manual advises as much.

Answer 2

您必须将函数定义为返回 set of sampletest，然后根据传递的参数返回 return different query restults。

CREATE FUNCTION
  test_dob_dates(_sd date, _ed date)
RETURNS
  SETOF sampletest
AS
  $BODY$
    BEGIN
      IF _sd IS NOT NULL AND _ed IS NOT NULL THEN
        RETURN QUERY SELECT * FROM sampletest WHERE dob BETWEEN _sd AND _ed;
      ELSIF _sd IS NULL AND _ed IS NULL THEN
        RETURN QUERY SELECT * FROM sampletest WHERE dob IS NULL;
      ELSEIF _ed IS NOT NULL THEN
        RETURN QUERY SELECT * FROM sampletest WHERE dob <= _ed;
      ELSE
        RETURN QUERY SELECT * FROM sampletest WHERE dob >= _sd;
      END IF;
    END;
  $BODY$
LANGUAGE
  'plpgsql' VOLATILE;

eid IS NOT NULL 子句似乎是多余的，因为您已经将 eid 定义为 PRIMARY KEY，这意味着它永远不能为 NULL。

Answer 3

SQL Fiddle

create function test_dob_dates(_sd date, _ed date)
returns setof sampletest as $body$
    select *
    from sampletest
    where
        eid is not null
        and (
            (_sd is null and _ed is null)
            or (_sd is not null and _ed is null and dob >= _sd)
            or (_sd is null and _ed is not null and dob <= _ed)
            or dob between _sd and _ed
        );
$body$ language sql stable;