sql - 如何在 ON CONFLICT 子句中消除 plpgsql 变量名的歧义？

Question

给定这张表:

create table test (
    name text primary key
);

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

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，但会抛出一个不明确的列引用:

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称指定为 on conflict (test.name) 不编译，或 ((test.name)) 编译:

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

有解决办法吗？

---

编辑:我找到了一个解决方法:

on conflict on constraint test_pkey do update

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

Answer 1

首先，name对变量和属性来说都是一个坏名字。当你同时拥有两者时，代码将不会好看。考虑到这一点，您可以使用带标签的 block “前缀”变量(在下面的示例中 <<fn>>``), and set variable_conflict` 以优先考虑列名，请参见下面的代码:

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

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.

而且 - 基本上整个链接都是关于它的。

然而 - 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:

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.