Remove usage of COALESCE from dashboard chart (#1306)

* Fix COALESCE timestamp generation

* Remove coalesce altogether

* Fix linting violation

---------

Co-authored-by: Ben Sheldon [he/him] <[email protected]>

Author: bananatron

app/charts/good_job/performance_index_chart.rb

@@ -5,7 +5,7 @@ class PerformanceIndexChart < BaseChart
     def data
       table_name = GoodJob::Execution.table_name
 
-      sum_query = Arel.sql(GoodJob::Job.pg_or_jdbc_query(<<~SQL.squish))
+      sum_query = <<~SQL.squish
         SELECT *
         FROM generate_series(
           date_trunc('hour', $1::timestamp),

app/charts/good_job/performance_show_chart.rb

@@ -21,7 +21,7 @@ def data
       table_name = GoodJob::Execution.table_name
 
       interval_entries = BUCKET_INTERVALS.map { "interval '#{_1}'" }.join(",")
-      sum_query = Arel.sql(GoodJob::Job.pg_or_jdbc_query(<<~SQL.squish))
+      sum_query = <<~SQL.squish
         SELECT
           WIDTH_BUCKET(duration, ARRAY[#{interval_entries}]) as bucket_index,
           COUNT(WIDTH_BUCKET(duration, ARRAY[#{interval_entries}])) AS count

app/charts/good_job/scheduled_by_queue_chart.rb

@@ -8,9 +8,7 @@ def initialize(filter)
     end
 
     def data
-      table_name = GoodJob::Job.table_name
-
-      count_query = Arel.sql(GoodJob::Job.pg_or_jdbc_query(<<~SQL.squish))
+      count_query = <<~SQL.squish
         SELECT *
         FROM generate_series(
           date_trunc('hour', $1::timestamp),
@@ -23,7 +21,7 @@ def data
               queue_name,
               count(*) AS count
             FROM (
-              #{@filter.filtered_query.except(:select, :order).select('queue_name', "COALESCE(#{table_name}.scheduled_at, #{table_name}.created_at)::timestamp AS scheduled_at").to_sql}
+              #{@filter.filtered_query.except(:select, :order).select(:queue_name, :scheduled_at).to_sql}
             ) sources
             GROUP BY date_trunc('hour', scheduled_at), queue_name
         ) sources ON sources.scheduled_at = timestamp