> On 31/05/2023 00:28 CEST Lian Jiang <jiangok2006@xxxxxxxxx> wrote: > > The info useful for me is command_tag, object_type, object_identity. > classid, objid is not useful since object_identity is more explicit. > objsubid is not useful because I don't need comment > (https://www.postgresql.org/message-id/Pine.LNX.4.33.0212091822050.15095-100000@xxxxxxxxxxxxxxx) > information for schema change. You need objsubid to identify the column in pg_attribute to get its type, not just to get the comment from pg_description as the linked thread says. > Besides table name, I still need: > * which columns are added and their types. > * which columns have type change, the old and new types. > * which columns are dropped. > > Will command field provide this info? I don't have an example and decoding it > needs C code (https://www.postgresql.org/message-id/20190712222343.GA26924%40alvherre.pgsql). > If I cannot get such info from pg_event_trigger_ddl_commands, I may need to > maintain schema snapshots myself and diff the old and new snapshots upon an > alter table/view event. Which way should I go? Thanks a lot. Right off the bat, I would combine it with a ddl_command_start event trigger to record the necessary info (current columns and their types) in a temp table. Query this table in the ddl_command_end event trigger to figure out which columns have changes. This can be done entirely in plpgsql without using the command column. -- Erik
