将密钥添加到空的hstore列 [英] Adding a key to an empty hstore column

问题描述

根据postgres文档，将密钥添加到hstore列，如下所示：

According to the postgres documentation, you add a key to an hstore column as follows:

UPDATE tab SET h = h || ('c' => '3');

但这似乎仅在hstore字段不为空的情况下有效。例如：

But it seems to only work if the hstore field is not empty. For example:

postgres=# create table htest (t text, h hstore);
CREATE TABLE
postgres=# insert into htest (t) VALUES ('key');
INSERT 0 1
postgres=# update htest set h = h || ('foo'=>'bar') where t='key';
UPDATE 1
postgres=# select * from htest;
  t  | h 
-----+---
 key | 
(1 row)

更新成功，但hstore未更新。但是：

The update was successful, yet the hstore was not updated. However:

postgres=# update htest set h = ('foo'=>'bar') where t='key';
UPDATE 1
postgres=# select * from htest;
  t  |      h       
-----+--------------
 key | "foo"=>"bar"
(1 row)

postgres=# update htest set h = h || ('bar'=>'foo') where t='key';
UPDATE 1
postgres=# select * from htest;
  t  |             h              
-----+----------------------------
 key | "bar"=>"foo", "foo"=>"bar"
(1 row)

是否可以在不先检查hstore是否为空的情况下自动向hstore添加密钥？

Is there a way to atomically add a key to an hstore without first checking if the hstore is empty?

推荐答案

我认为这里的问题是您拥有的hstore为null，并且null或某些hstore为null。

I think the problem here is that the hstore you have is null, and null OR some hstore is null.

我有最好的解决方案，可能不是最好的解决方案是使表具有默认的空hstore而不是允许为null。然后，您的示例将按照您的意愿进行工作：

The best solution I have, which is probably not the best solution, is to make the table with a default empty hstore rather than allowing null. Then your examples work as you would like:

postgres=# create table htest (t text, h hstore default hstore(array[]::varchar[]));
CREATE TABLE
postgres=# insert into htest (t) values ('key');
INSERT 0 1
postgres=# update htest set h = h || ('foo'=>'bar') where t='key';
UPDATE 1
postgres=# select * from htest;
  t  |      h       
-----+--------------
 key | "foo"=>"bar"
(1 row)

我很遗憾没有与 hstore（array [] :: varchar []）相比，可以找到一种更干净的创建空hstore的方法，但这并不意味着没有更好的方法。您可以像以前这样将其合并到您的hstore更新中：

I unfortunately do not see a cleaner way to create an empty hstore than hstore(array[]::varchar[]) but that doesn't mean there isn't a better way. You could incorporate this into your hstore update from before like so:

update htest set h = coalesce(h, hstore(array[]::varchar[])) || ('foo'=>'bar') where t='key';

这样，您无需重新创建表。我发现那相当粗暴。希望这会有所帮助。

This way you don't need to recreate the table. I find that fairly gross though. Hope this helps.

这篇关于将密钥添加到空的hstore列的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！