Arrays 复制具有动态列名的记录
我在PostgreSQL 9.3中有两个不同列的表:Arrays 复制具有动态列名的记录,arrays,postgresql,variables,plpgsql,dynamic-sql,Arrays,Postgresql,Variables,Plpgsql,Dynamic Sql,我在PostgreSQL 9.3中有两个不同列的表: CREATE TABLE person1( NAME TEXT NOT NULL, AGE INT NOT NULL ); CREATE TABLE person2( NAME TEXT NOT NULL, AGE INT NOT NULL, ADDRESS CHAR(50), S
CREATE TABLE person1(
NAME TEXT NOT NULL,
AGE INT NOT NULL
);
CREATE TABLE person2(
NAME TEXT NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR(50),
SALARY REAL
);
INSERT INTO person2 (Name, Age, ADDRESS, SALARY)
VALUES ('Piotr', 20, 'London', 80);
我想将记录从person2
复制到person1
,但列名可能会在程序中更改,因此我想在程序中选择联合列名。因此,我创建了一个包含列名交集的数组。接下来我使用一个函数:insert-into。。。。选择
,但当我按名称将数组变量传递给函数时,会出现错误。像这样:
select column_name into name1 from information_schema.columns where table_name = 'person1';
select column_name into name2 from information_schema.columns where table_name = 'person2';
select * into cols from ( select * from name1 intersect select * from name2) as tmp;
-- Create array with name of columns
select array (select column_name::text from cols) into cols2;
CREATE OR REPLACE FUNCTION f_insert_these_columns(VARIADIC _cols text[])
RETURNS void AS
$func$
BEGIN
EXECUTE (
SELECT 'INSERT INTO person1 SELECT '
|| string_agg(quote_ident(col), ', ')
|| ' FROM person2'
FROM unnest(_cols) col
);
END
$func$ LANGUAGE plpgsql;
select * from cols2;
array
------------
{name,age}
(1 row)
SELECT f_insert_these_columns(VARIADIC cols2);
这里出了什么问题?您似乎认为SQL中的
SELECT-INTO
会分配一个变量。但事实并非如此
它创建了一个新的表,不鼓励在Postgres中使用它。使用上级创建表作为
。不仅如此,因为plpgsql内部的SELECT INTO
的含义不同:
SELECT f_insert_these_columns(VARIADIC cols2);
或清洁剂:
SELECT f_insert_these_columns(VARIADIC array) -- "array" being the unfortunate column name
FROM cols2
LIMIT 1;
关于short表
语法:
CREATE OR REPLACE FUNCTION f_copy_rows_with_shared_cols(
IN _tbl1 regclass
, IN _tbl2 regclass
, OUT rows int
, OUT columns text)
LANGUAGE plpgsql AS
$func$
BEGIN
SELECT INTO columns -- proper use of SELECT INTO!
string_agg(quote_ident(attname), ', ')
FROM (
SELECT attname
FROM pg_attribute
WHERE attrelid IN (_tbl1, _tbl2)
AND NOT attisdropped -- no dropped (dead) columns
AND attnum > 0 -- no system columns
GROUP BY 1
HAVING count(*) = 2
) sub;
EXECUTE format('INSERT INTO %1$s(%2$s) SELECT %2$s FROM %3$s'
, _tbl1, columns, _tbl2);
GET DIAGNOSTICS rows = ROW_COUNT; -- return number of rows copied
END
$func$;
电话:
结果:
rows | columns
-----+---------
3 | name, age
要点
- 注意在plpgsql中正确使用
进行赋值SELECT INTO
- 注意数据类型
的使用。这允许使用模式限定表名(可选),并防止SQL注入尝试:regclass
- 关于获取诊断信息:
- 关于
参数:OUT
CREATE OR REPLACE FUNCTION f_copy_rows_with_shared_cols(
IN _tbl1 regclass
, IN _tbl2 regclass
, OUT rows int
, OUT columns text)
LANGUAGE plpgsql AS
$func$
BEGIN
SELECT INTO columns -- proper use of SELECT INTO!
string_agg(quote_ident(attname), ', ')
FROM (
SELECT attname
FROM pg_attribute
WHERE attrelid IN (_tbl1, _tbl2)
AND NOT attisdropped -- no dropped (dead) columns
AND attnum > 0 -- no system columns
GROUP BY 1
HAVING count(*) = 2
) sub;
EXECUTE format('INSERT INTO %1$s(%2$s) SELECT %2$s FROM %3$s'
, _tbl1, columns, _tbl2);
GET DIAGNOSTICS rows = ROW_COUNT; -- return number of rows copied
END
$func$;
SELECT * FROM f_copy_rows_with_shared_cols('public.person2', 'public.person1');
rows | columns
-----+---------
3 | name, age