创建函数时的 Postgres 错误

Question

我正在尝试在 Postgres 中创建一个函数，如下所示：

Create function Samplefunc() 
returns resultdata( Tested int, Score int,
       Growth int) as
$BODY$
Select 
       Count(distinct student_id) Tested, 
       Cast(Avg(R.raw_score) as Int)  Score,
       Avg(R.growth) as Growth
from results R
where R.id=1 and test_id='ME04';
$BODY$
LANGUAGE sql;

但我收到以下错误：

ERROR:  syntax error at or near "int"
LINE 2: returns resultdata( NTested int, RawScore int,
                                    ^

********** Error **********

ERROR: syntax error at or near "int"
SQL state: 42601
Character: 59

我哪里错了？

Answer 1

CREATE FUNCTION samplefunc() 
  RETURNS TABLE(ntested int, rawscore int, growth int) AS
$func$
SELECT count(DISTINCT r.student_id) -- AS NTested
      ,avg(r.raw_score)::int        -- AS RawScore
      ,avg(r.growth)::int           -- AS Growth
FROM   reports_results r
WHERE  r.test_type_id = 1
AND    r.test_id = '201403MAME04'
$func$ LANGUAGE sql;

• 返回表的子句是RETURNS TABLE。

• 小心避免OUT 参数和列名之间的冲突。 （我的初稿中有这样的冲突）。表限定列以消除歧义。 RETURNS TABLE 中的所有字段名称实际上都是 OUT 参数，并且在函数内（几乎）随处可见。

还有：

• avg(growth) 将导致类型与声明的返回类型 int 不匹配。你也需要投射它。使用简短的Postgres-specific syntax ::type，顺便说一句。
  更好的是：返回 numeric or a floating point number 以保留平均数字中的小数位数。

• 列别名仅在函数内部可见。如果您不打算在函数内部引用它们，它们只是文档。

• 大写是怎么回事？ Unquoted identifiers are cast to lower case in Postgres automatically.

如果保证查询返回单个行，您可能希望将OUT参数与RETURNS record结合起来：

CREATE FUNCTION samplefunc(OUT ntested int, OUT rawscore int, OUT growth int) 
  RETURNS record  AS ...

细微的差别：这样一来，如果没有找到任何内容，您将获得带有 NULL 值的单行，而第一个表单将不返回任何内容/没有行。

添加 IN 参数（在评论中请求）

CREATE FUNCTION samplefunc(_test_type_id int, _test_id text) 
  RETURNS TABLE(ntested int, rawscore int, growth int) AS
$func$
SELECT count(DISTINCT r.student_id)
      ,avg(r.raw_score)::int
      ,avg(r.growth)::int
FROM   reports_results r
WHERE  r.test_type_id = $1   -- or: = _test_type_id in Postgres 9.2+
AND    r.test_id = $2        -- or: = _test_id
$func$ LANGUAGE sql;

这里有很多关于 SO 的相关答案以及更多代码示例。喜欢：

• PostgreSQL return a function with a Custom Data Type

Try a search.

Answer 2

尽量不要指定复合返回类型的细节。但是，我认为回报结构必须首先存在。

Create table resultdata (NTested int, RawScore int, Growth int);

Create function Samplefunc() returns resultdata as
$BODY$
Select 
   Count(distinct student_id) as NTested, 
   Cast(Avg(R.raw_score) as Int) as RawScore,
   Avg(R.growth) as Growth
from reports_results R
where R.test_type_id=1 and test_id='201403MAME04';
$BODY$
LANGUAGE sql;

或者尝试显式返回一个表：

Create function Samplefunc() 
    returns Table (NTested int, RawScore int, Growth int) as
$BODY$
Select 
   Count(distinct student_id) as NTested, 
   Cast(Avg(R.raw_score) as Int) as RawScore,
   Avg(R.growth) as Growth
from reports_results R
where R.test_type_id=1 and test_id='201403MAME04';
$BODY$
LANGUAGE sql;

我认为你也可以使用输出参数返回一组记录：

Create function Samplefunc(OUT NTested int, OUT RawScore int, OUT Growth int) 
    returns SetOf Record as
$BODY$
Select 
   Count(distinct student_id) as NTested, 
   Cast(Avg(R.raw_score) as Int) as RawScore,
   Avg(R.growth) as Growth
from reports_results R
where R.test_type_id=1 and test_id='201403MAME04';
$BODY$
LANGUAGE sql;

Answer 3

您正在尝试返回包含多个输出参数的记录。你应该这样做：

Create function Samplefunc(out NTested int, out RawScore int, out Growth int) as
$BODY$
Select 
       Count(distinct student_id) NTested, 
       Cast(Avg(R.raw_score) as Int)  RawScore,
       Avg(R.growth) as Growth
from reports_results R
where R.test_type_id=1 and test_id='201403MAME04';
$BODY$
LANGUAGE sql;

您可以使用显式命名的复合类型更详细地执行相同的操作；喜欢

CREATE TYPE resultdata AS (NTested int, RawScore int, Growth int);

CREATE FUNCTION Samplefunc() RETURNS resultdata
    AS .......

或使用TABLE 之类的函数

CREATE FUNCTION Samplefunc() RETURNS TABLE(NTested int, RawScore int, Growth int)
AS
......

有关更多信息，请参阅PostgreSQL Documentation

Answer 4

如果您没有像 Luke 正确假设的那样定义类型“结果集”，请尝试返回一个表。

Create function Samplefunc() 
returns table( NTested int, RawScore int,
       Growth int) as
$BODY$
Select 
       Count(distinct student_id) NTested, 
       Cast(Avg(R.raw_score) as Int)  RawScore,
       Avg(R.growth) as Growth
from reports_results R
where R.test_type_id=1 and test_id='201403MAME04';
$BODY$
LANGUAGE sql;