返回行匹配PLPGSQL功能输入数组中的元素 [英] Return rows matching elements of input array in plpgsql function
问题描述
我想创建一个PostgreSQL函数,它类似如下:
I would like to create a PostgreSQL function that does something like the following:
CREATE FUNCTION avg_purchases( IN last_names text[] DEFAULT '{}' )
RETURNS TABLE(last_name text[], avg_purchase_size double precision)
AS
$BODY$
DECLARE
qry text;
BEGIN
qry := 'SELECT last_name, AVG(purchase_size)
FROM purchases
WHERE last_name = ANY($1)
GROUP BY last_name'
RETURN QUERY EXECUTE qry USING last_names;
END;
$BODY$
不过,我在这里看到了两个问题:
But I see two problems here:
- 现在还不清楚,我认为数组类型是输入的最有用的类型。
-
这是目前返回零行,当我做的:
- It is not clear to me that array type is the most useful type of input.
This is currently returning zero rows when I do:
SELECT avg_purchases($${'Brown','Smith','Jones'}$$);
我是什么失踪?
推荐答案
这个作品:
CREATE OR REPLACE FUNCTION avg_purchases(last_names text[] = '{}')
RETURNS TABLE(last_name text, avg_purchase_size float8)
AS
$func$
SELECT last_name, AVG(purchase_size)::float8
FROM purchases
WHERE last_name = ANY($1)
GROUP BY last_name
$func$ LANGUAGE sql;
电话:
SELECT * FROM avg_purchases('{foo,Bar,baz,"}weird_name''$$"}');
或(更新 - 例如使用<一个href=\"http://www.postgresql.org/docs/current/interactive/sql-syntax-lexical.html#SQL-SYNTAX-DOLLAR-QUOTING\"相对=nofollow>美元符):
Or (update - example with dollar-quoting):
SELECT * FROM avg_purchases($x${foo,Bar,baz,"}weird_name'$$"}$x$);
-
更多关于如何报价字符串:结果
<一href=\"http://stackoverflow.com/questions/12316953/insert-varchar-with-single-quotes-in-postgresql/12320729#12320729\">Insert VARCHAR与PostgreSQL中单引号您不需要在这里的动态SQL。
You don't need dynamic SQL here.
虽然你的可以的把它包装成一个PLPGSQL功能(这可能是有用的),一个简单的SQL函数做的工作就好了。
While you can wrap it into a plpgsql function (which may be useful), a simple SQL function is doing the job just fine.
您的类型不匹配
-
的平均结果()
可数字
持有precise结果。我投以的float8
,使其工作,这仅仅是双precision
别名(可以使用其一)。如果你需要完美的precision,使用数字
代替。 - 既然你
GROUP BY姓氏
你想要一个简单的文本
OUT参数,而不是正文[]
。
- the result of
avg()
may benumeric
to hold a precise result. I cast tofloat8
to make it work, which is just an alias fordouble precision
(you can use either). If you need perfect precision, usenumeric
instead. - Since you
GROUP BY last_name
you want a plaintext
OUT parameter instead oftext[]
.
数组被输入的一个有用的类型。如果您的客户端更容易,你也可以使用<一个href=\"http://www.postgresql.org/docs/current/interactive/xfunc-sql.html#XFUNC-SQL-VARIADIC-FUNCTIONS\"相对=nofollow>
可变参数
输入参数,允许传递数组作为元素的列表:An array is a useful type of input. If it's easier for your client you can also use a
VARIADIC
input parameter that allows to pass the array as a list of elements:CREATE OR REPLACE FUNCTION avg_purchases(VARIADIC last_names text[] = '{}') RETURNS TABLE(last_name text, avg_purchase_size float8) AS $func$ SELECT last_name, AVG(purchase_size)::float8 FROM purchases JOIN (SELECT unnest($1)) t(last_name) USING (last_name) GROUP BY last_name $func$ LANGUAGE sql
电话:
SELECT * FROM avg_purchases('foo', 'Bar', 'baz', '"}weird_name''$$"}');
或(使用美元符):
SELECT * FROM avg_purchases('foo', 'Bar', 'baz', $y$'"}weird_name'$$"}$y$);
请注意,标准的Postgres只允许一个最多100个元素的。这是在编译时由 preSET确定选项:
max_function_args(整数)
报告函数参数的最大数量。它是由
FUNC_MAX_ARGS
价值建立服务器时确定。默认值是100的参数。Reports the maximum number of function arguments. It is determined by the value of
FUNC_MAX_ARGS
when building the server. The default value is 100 arguments.您仍然可以使用数组方式调用它时$ P $用关键字
可变参数
pfixed:You can still call it with array notation when prefixed with the keyword
VARIADIC
:SELECT * FROM avg_purchases(VARIADIC '{1,2,3, ... 99,100,101}');
对于更大的阵列(100+),我也用的
UNNEST()
子查询和加入
给它,这往往能够更好地扩展For bigger arrays (100+), I would also use
unnest()
in a subquery andJOIN
to it, which tends to scale better:- Optimizing a Postgres query with a large IN
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