Re: Determining table change in an event trigger

On 08/24/2016 12:58 AM, Alvaro Herrera wrote:
> Jonathan Rogers wrote:
>> I am trying to use an event trigger to do something when a column
>> changes. I can declare an event trigger "ON sql_drop WHEN TAG IN ('ALTER
>> TABLE')" to get dropped columns. However, I can't figure out any good
>> way to determine when a column has been added or altered.
>>
>> I can declare an event trigger "ON ddl_command_end WHEN TAG IN ('ALTER
>> TABLE')" but that gets unwanted events such as disabling triggers on a
>> table. Function pg_event_trigger_ddl_commands() returns rows with column
>> "command" of type "pg_ddl_command" which contains "a complete
>> representation of the command, in internal format." According to the
>> docs, this cannot be output directly, but it can be passed to other
>> functions to obtain different pieces of information about the command.
>> However, I cannot find any other functions which operate on the type
>> pg_ddl_command. Am I missing something? Is the documentation lacking?
>
> Yeah, that type can only be processed by C functions. You'd need to
> write a C function to examine the structure and see whether it matches
> what you need.
>

OK, thanks for the explanation. It seems like the docs should make it
clear that the "other functions" are not included.

--
Jonathan Rogers
Socialserve.com by Emphasys Software
jrogers(at)emphasys-software(dot)com