Tsvectors for multiple search methods

[darrenb...@gmail.com]

I'm trying to setup tsvector columns for a scope search with tsearch, trigram, and dmetaphone.  The documentation says:

• Create a column of type tsvector that you'd like to search against. If you want to search using multiple search methods, for example tsearch and dmetaphone, you'll need a column for each.
• Create a trigger function that will update the column(s) using the expression appropriate for that type of search. See: the PostgreSQL documentation for text search triggers

What is the purpose of setting up multiple tsvector columns vs just having one and using it for each type of search? I understand how to build a tsvector for tsearch from the docs, but how do you go about setting up a trigger expression for a dmetaphone?  

[Grant Hutchins]

We have a (somewhat incomplete) wiki page about building indexes.

You will want to make a tsvector based on each expression that pg_search generates for your document. So you might notice that the expression for the dmetaphone part includes a call to pg_search_dmetaphone() mixed in somewhere between all the to_tsvector calls, the coalesce calls, any unaccent() calls, etc.

The main reason you need to have separate tsvectors is that the different expressions for the document part of the @@ parts of the where clause end up generating completely different tsvectors.

I hope this helps, I know it's a bit esoteric. Feel free to ask follow-up questions.

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[blev...@mdsol.com]

I have the same question. It's not clear to me what the expression should be for a dmetaphone tsvector column. Is there an example somewhere that shows what the trigger code should be? Thanks!