Join against the output of an array unnest without creating a temp table

Question

I have a query in a UDF (shown below) which unnest()s an array of integers and joins against it, I have created a local temp table in my pgplsql UDF since I know this works. Is it possible to use unnest directly in a query to perform a join instead of having to create a temp table ?

CREATE OR REPLACE FUNCTION search_posts(
    forum_id_ INTEGER,
    query_ CHARACTER VARYING,
    offset_ INTEGER DEFAULT NULL,
    limit_ INTEGER DEFAULT NULL,
    from_date_ TIMESTAMP WITHOUT TIME ZONE DEFAULT NULL,
    to_date_ TIMESTAMP WITHOUT TIME ZONE DEFAULT NULL,
    in_categories_ INTEGER[] DEFAULT '{}'
    )
RETURNS SETOF forum_posts AS $$
DECLARE
    join_string CHARACTER VARYING := ' ';
    from_where_date CHARACTER VARYING := ' ';
    to_where_date CHARACTER VARYING := ' ';
    query_string_ CHARACTER VARYING := ' ';
    offset_str_ CHARACTER VARYING := ' ';
    limit_str_ CHARACTER VARYING := ' ';
BEGIN
    IF NOT from_date_ IS NULL THEN
        from_where_date := ' AND fp.posted_at > ''' || from_date_ || '''';
    END IF;

    IF NOT to_date_ IS NULL THEN
        to_where_date := ' AND fp.posted_at < ''' || to_date_ || '''';
    END IF;

    IF NOT offset_ IS NULL THEN
        offset_str_ := ' OFFSET ' || offset_; 
    END IF;

    IF NOT limit_ IS NULL THEN
        limit_str_ := ' LIMIT ' || limit_;
    END IF;

    IF NOT limit_ IS NULL THEN
    END IF;

    CREATE LOCAL TEMP TABLE un_cat(id) ON COMMIT DROP AS (select * from unnest(in_categories_)) ;

    if in_categories_ != '{}' THEN
        join_string := ' INNER JOIN un_cat uc ON uc.id = fp.category_id ' ;
    END IF;
s
    query_string_ := '
    SELECT fp.*
    FROM forum_posts fp' ||
        join_string
    ||
    'WHERE fp.forum_id = ' || forum_id_ || ' AND
    to_tsvector(''english'',fp.post_text) @@ to_tsquery(''english'','''|| query_||''')' || 
        from_where_date || 
        to_where_date ||
        offset_str_ ||
        limit_str_ 
    ||  ';';

    RAISE NOTICE '%', query_string_;
    
    RETURN QUERY
    EXECUTE query_string_;
END;
$$ LANGUAGE plpgsql;

    
select * from search_posts(forum_id_:=1, query_:='scout & rampage', in_categories_ := '{71}');

The reason I want to do this is that I want to be able to have a look at the query plan without having to resort to look at the auto_explain output in the server log.

A local temp table prevents this. I.e., I can't copy paste the resulting query and execute it verbatim.

Answer 1

Is it possible to use unnest() directly in a query to perform a join instead of having to create a temp table?

Yes, and it is typically much more efficient:

SELECT *
FROM   tbl t
JOIN   unnest('{10,11,12}'::int[]) AS x(tbl_id) USING (tbl_id);