Don't skip some columns in column_types on Postgres

[ghiculescu]

Fixes #41651, by partially reverting #39097. I just reverted the line that @terracatta highlighted as problematic.

I ran the same benchmark as #39097 and it seems like this change does not cause a perf regression.

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails", path: "/Users/alex/code/rails" # github: "rails/rails", branch: "main"
  gem "sqlite3"
  gem "benchmark-ips"
end

require "active_record"

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")

ActiveRecord::Schema.define do
  create_table :active_storage_blobs do |t|
    t.string   :key,          null: false
    t.string   :filename,     null: false
    t.string   :content_type
    t.text     :metadata
    t.string   :service_name, null: false
    t.bigint   :byte_size,    null: false
    t.string   :checksum,     null: false
    t.datetime :created_at,   null: false

    t.index [ :key ], unique: true
  end
end

class ActiveStorageBlob < ActiveRecord::Base
end

Benchmark.ips do |x|
  x.report("find_by") { ActiveStorageBlob.find_by(id: 1) }
end

This branch:

Warming up --------------------------------------
             find_by     1.940k i/100ms
Calculating -------------------------------------
             find_by     17.928k (± 4.8%) i/s -     91.180k in   5.098301s

Main:

Warming up --------------------------------------
             find_by     1.912k i/100ms
Calculating -------------------------------------
             find_by     17.961k (± 4.8%) i/s -     89.864k in   5.015252s

So it's basically the same. cc @terracatta @boblail

[ghiculescu]

This is a bit yucky, but it only happens in very specific cases: if you have select two (or more) columns that don't have an alias and use the same SQL function (eg COALESCE). This happens because of how Postgres returns column names, see #36186 (comment) for a summary.

As far as I can tell we have a few options:

• The current state, which results in this bug: ActiveRecord::Result#column_types is often missing data #41651
• This PR, which fixes ActiveRecord::Result#column_types is often missing data #41651 but introduces this inconsistency between databases.
• Implement the refactor in Avoid coercing all SELECTs with the same column name to the same value #36186, which adds a fair bit of overhead to every query for a relatively niche issue.

In my opinion this PR is the least bad option.

[rails-bot]

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