如何在ON CONFLICT子句中消除plpgsql变量名称的歧义? [英] How to disambiguate a plpgsql variable name in a ON CONFLICT clause?

问题描述

给出此表:

create table test (
    name text primary key
);

我需要编写一个plpgsql函数，其变量名与主键名冲突，必须在on conflict子句中使用它:

I need to write a plpgsql function with a variable name that collides with the primary key name, which I must use in a on conflict clause:

create or replace function func(
    name text                               -- this variable name...
) returns void language plpgsql as 
$$
begin 
    insert into test (name) values (name) 
    on conflict (name) do update            -- ...conflicts with this line
    set name = func.name; 
end; 
$$;

这会编译，但是会抛出一个含糊的列引用:

This compiles, but then throws an ambiguous column reference:

select * from func('one');
ERROR:  column reference "name" is ambiguous
LINE 2:     on conflict (name) do update 
                        ^
DETAIL:  It could refer to either a PL/pgSQL variable or a table column.
QUERY:  insert into test (name) values (name) 
    on conflict (name) do update 
    set name = func.name
CONTEXT:  PL/pgSQL function func(text) line 3 at SQL statement

我尝试将完整的列名指定为不编译的on conflict (test.name)或编译的((test.name)):

I tried specifying the full column name as on conflict (test.name) which does not compile, or ((test.name)) which compiles:

create or replace function func(
    name text
) returns void language plpgsql as 
$$
begin 
    insert into test (name) values (name) 
    on conflict ((test.name)) do            -- this fails too
    update set name = func.name; 
end; 
$$;

但是它也失败了:

select * from func('two');
ERROR:  invalid reference to FROM-clause entry for table "test"
LINE 2:     on conflict ((test.name)) do 
                          ^
HINT:  There is an entry for table "test", but it cannot be referenced from this part of the query.
QUERY:  insert into test (name) values (name) 
    on conflict ((test.name)) do 
    update set name = func.name
CONTEXT:  PL/pgSQL function func(text) line 3 at SQL statement

有解决方案吗?

我找到了一种解决方法:

I found a workaround:

on conflict on constraint test_pkey do update

其中，test_pkey是表名加_pkey.我不知道这有多可靠.我仍然想改为指定列名.

where test_pkey is the table name plus _pkey. I don't know how reliable this is though. I'd still like to specify the column name instead.

推荐答案

首先，对于变量和属性，name都是一个不好的名字.两者兼而有之时，代码将看起来不那么好.考虑到这一点，您可以在变量前加上带标签的块(例如在<<fn>>``), and set variable_conflict`下面的示例中，以优先选择列名，请参见下面的代码:

to start with, name is a bad name for both variable and attribute. When you have both, code won't look good. with that in mind, you can "prefix" variable with labeled block (in example below <<fn>>``), and setvariable_conflict` to give preference to column name, see code below:

t=# create or replace function func(
    name text
) returns void language plpgsql as
$$
#variable_conflict use_column
<<fn>>
declare name text :='blah';
begin
    insert into test (name) values (name)
    on conflict (name) do            -- this no longer fails
    update set name = fn.name;
end;
$$;
t=# insert into test select 'b';
INSERT 0 1
Time: 8.076 ms
t=# select func('b');
 func
------

(1 row)

Time: 6.117 ms
t=# select * from test;
 name
------
 b
 blah
(2 rows)

https://www.postgresql .org/docs/current/static/plpgsql-implementation.html#PLPGSQL-VAR-SUBST

默认情况下，如果SQL语句中的名称，PL/pgSQL将报告错误 可以引用变量或表列.您可以解决这样的问题 通过重命名变量或列，或通过限定 模棱两可的引用，或通过告诉PL/pgSQL对哪个解释 喜欢.

By default, PL/pgSQL will report an error if a name in a SQL statement could refer to either a variable or a table column. You can fix such a problem by renaming the variable or column, or by qualifying the ambiguous reference, or by telling PL/pgSQL which interpretation to prefer.

，进一步-基本上整个链接都是关于它的.

and further - basically the whole link is about it.

但是-在演示了如何使用plpgsql轻松完成特定任务之后，我仍然引用namual:

And yet - after demonstrating how particular task this can be easily done with plpgsql, I still quote namual:

最简单的解决方案是重命名变量或列.普通的 编码规则是对PL/pgSQL使用不同的命名约定 变量，而不是用于列名的变量.例如，如果您 一致地命名函数变量v_something，而您都没有 列名称以v_开头，不会发生冲突.

The simplest solution is to rename the variable or column. A common coding rule is to use a different naming convention for PL/pgSQL variables than you use for column names. For example, if you consistently name function variables v_something while none of your column names start with v_, no conflicts will occur.

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