Pre-join Projections

edited June 2017 in General Discussion

I know the basic use of projections after going through the documentation. I am trying to create this projection but it says, "Only ONE table or projection is allowed in the FROM clause of aggregate projection". Here's what I am trying to do:

CREATE PROJECTION public.fct_asx_star_coverages_test_count_per_source
dim_star_coverage_files_source ENCODING RLE,
dim_module_suite_fk ENCODING RLE
select dim.dim_star_coverage_files_source, count(fct.dim_module_suite_fk) from fct_asx_star_coverages fct, dim_star_coverage_files dim
WHERE fct.dim_star_coverage_files_fk = dim.dim_star_coverage_files_sk
GROUP BY dim.dim_star_coverage_files_source;



  • [Deleted User][Deleted User] Administrator

    Prejoin projections are deprecated in Vertica 8.0 and higher and I would not encorage you to use them .
    If you really care, prejoin projections can't have aggregrations but simple join between two tables haveing PK-FK relationship .
    You are trying to create is a live aggregate projections in Vertica but that does not support join between tables and that is the reason you are getting above error .

  • Thank you @skamat
    I recently started testing Vertica. I have a fact table with 8 mil rows. It is just joined with two dimensions. forming a star schema. The above SELECT statement takes approximately 38 seconds to show process the query. What can I do to optimize this query performance? Any tips?

  • there's nothing you can do to optimize this. vertica does not scale well with joins 1M up in my experience. there's just no way out of it.

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