[英]PL/Python & postgreSQL: What is the best way to return a table of many columns?
In Pl/Python "RETURNS setof" or "RETURNS table" clause are used to return a table like structured data. 在Pl / Python中,“ RETURNS setof”或“ RETURNS table”子句用于返回类似于结构化数据的表。 It seems to me that one has to provide the name of each column to get a table returned.
在我看来,必须提供每一列的名称才能返回表。 If you have a table with a few columns it is an easy thing.
如果您的表有几列,这是一件容易的事。 However, if you have a table of 200 columns, what's the best way to do that?
但是,如果您有一个包含200列的表,那么执行此操作的最佳方法是什么? Do I have to type the names of all of columns (as shown below) or there is a way to get around it?
我是否必须键入所有列的名称(如下所示),还是有一种解决方法? Any help would be much appreciated.
任何帮助将非常感激。
Below is an example that uses "RETURNS table" clause. 下面是一个使用“ RETURNS table”子句的示例。 The code snippets creates a table (mysales) in postgres, populate it and then use Pl/Python to fetch it and returning the column values.
代码段在postgres中创建一个表(mysales),将其填充,然后使用Pl / Python来获取该表并返回列值。 For simplicity I am only returning 4 columns from the table.
为简单起见,我仅从表中返回4列。
DROP TABLE IF EXISTS mysales;
CREATE TABLE mysales (id int, year int, qtr int, day int, region
text) DISTRIBUTED BY (id);
INSERT INTO mysales VALUES
(1, 2014, 1,1, 'north america'),
(2, 2002, 2,2, 'europe'),
(3, 2014, 3,3, 'asia'),
(4, 2010, 4,4, 'north-america'),
(5, 2014, 1,5, 'europe'),
(6, 2009, 2,6, 'asia'),
(7, 2002, 3,7, 'south america');
DROP FUNCTION IF EXISTS myFunc02();
CREATE OR REPLACE FUNCTION myFunc02()
RETURNS TABLE (id integer, x integer, y integer, s text) AS
$$
rv = plpy.execute("SELECT * FROM mysales ORDER BY id", 5)
d = rv.nrows()
return ( (rv[i]['id'],rv[i]['year'], rv[i]['qtr'], rv[i]['region'])
for i in range(0,d) )
$$ LANGUAGE 'plpythonu';
SELECT * FROM myFunc02();
#Here is the output of the SELECT statement:
1; 2014; 1;"north america"
2; 2002; 2;"europe"
3; 2014; 3;"asia"
4; 2010; 4;"north-america"
5; 2014; 1;"europe"
6; 2009; 2;"asia"
7; 2002; 3;"south america"
Try this: 尝试这个:
CREATE OR REPLACE FUNCTION myFunc02()
RETURNS TABLE (like mysales) AS
$$
rv = plpy.execute('SELECT * FROM mysales ORDER BY id;', 5)
d = rv.nrows()
return rv[0:d]
$$ LANGUAGE 'plpythonu';
which returns: 返回:
gpadmin=# SELECT * FROM myFunc02();
id | year | qtr | day | region
----+------+-----+-----+---------------
1 | 2014 | 1 | 1 | north america
2 | 2002 | 2 | 2 | europe
3 | 2014 | 3 | 3 | asia
4 | 2010 | 4 | 4 | north-america
5 | 2014 | 1 | 5 | europe
(5 rows)
Something to consider for MPP like Greenplum and HAWQ is to strive for functions that take data as an argument and return a result, rather than originating the data in the function itself. 对于MPP(例如Greenplum和HAWQ),需要考虑的事情是争取将数据作为参数并返回结果的函数,而不是在函数本身中发起数据。 The same code executes on every segment so occasionally there can be unintended side effects.
相同的代码在每个段上执行,因此偶尔会有意外的副作用。
Update for SETOF
variant: SETOF
变体的更新:
CREATE TYPE myType AS (id integer, x integer, y integer, s text);
CREATE OR REPLACE FUNCTION myFunc02a()
RETURNS SETOF myType AS
$$
# column names of myType ['id', 'x', 'y', 's']
rv = plpy.execute("SELECT id, year as x, qtr as y, region as s FROM mysales ORDER BY id", 5)
d = rv.nrows()
return rv[0:d]
$$ LANGUAGE 'plpythonu';
Note, to use the same data from the original example, I had to alias each of the columns to corresponding names in myType
. 注意,要使用原始示例中的相同数据,我必须将每列的别名都命名为
myType
相应名称。 Also, you'll have to enumerate all of the columns of mysales
if going this route - there isn't a straightforward way to CREATE TYPE foo LIKE tableBar
although you might be able to use this to alleviate some of the manual work of enumerate all the names/types: 此外,如果要使用此路线,则必须枚举
mysales
所有列-尽管可以使用此方法来减轻一些枚举全部的手动工作,但没有一种直接CREATE TYPE foo LIKE tableBar
方法。名称/类型:
select string_agg(t.attname || ' ' || t.format_type || ', ') as columns from
(
SELECT a.attname,
pg_catalog.format_type(a.atttypid, a.atttypmod),
(SELECT substring(pg_catalog.pg_get_expr(d.adbin, d.adrelid) for 128)
FROM pg_catalog.pg_attrdef d
WHERE d.adrelid = a.attrelid AND d.adnum = a.attnum AND a.atthasdef),
a.attnotnull, a.attnum,
a.attstorage ,
pg_catalog.col_description(a.attrelid, a.attnum)
FROM pg_catalog.pg_attribute a
LEFT OUTER JOIN pg_catalog.pg_attribute_encoding e
ON e.attrelid = a .attrelid AND e.attnum = a.attnum
WHERE a.attrelid = (SELECT oid FROM pg_class WHERE relname = 'mysales') AND a.attnum > 0 AND NOT a.attisdropped
ORDER BY a.attnum
) t ;
which returns: 返回:
columns
-------------------------------------------------------------------
id integer, year integer, qtr integer, day integer, region text,
(1 row)
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