Hardened "add" arithmetic for usage data

Deals with  negative numbers and SQL exports

changelogs/unreleased/322099-sql-definition-for-template_repositories.yml

+---
+title: Hardened "add" arithmetic for usage data
+merge_request: 54794
+author:
+type: performance

lib/gitlab/usage_data_queries.rb

@@ -32,6 +32,10 @@ def estimate_batch_distinct_count(relation, column = nil, *rest)
         raw_sql(relation, column, :distinct)
       end
 
+      def add(*args)
+        'SELECT ' + args.map {|arg| "(#{arg})" }.join(' + ')
+      end
+
       private
 
       def raw_sql(relation, column, distinct = nil)

lib/gitlab/utils/usage_data.rb

@@ -86,6 +86,14 @@ def sum(relation, column, batch_size: nil, start: nil, finish: nil)
         FALLBACK
       end
 
+      def add(*args)
+        return -1 if args.any?(&:negative?)
+
+        args.sum
+      rescue StandardError
+        FALLBACK
+      end
+
       def alt_usage_data(value = nil, fallback: FALLBACK, &block)
         if block_given?
           yield

spec/lib/gitlab/usage_data_queries_spec.rb

@@ -38,4 +38,12 @@
       expect(described_class.sum(Issue, :weight)).to eq('SELECT SUM("issues"."weight") FROM "issues"')
     end
   end
+
+  describe '.add' do
+    it 'returns the combined raw SQL with an inner query' do
+      expect(described_class.add('SELECT COUNT("users"."id") FROM "users"',
+                                 'SELECT COUNT("issues"."id") FROM "issues"'))
+        .to eq('SELECT (SELECT COUNT("users"."id") FROM "users") + (SELECT COUNT("issues"."id") FROM "issues")')
+    end
+  end
 end

spec/lib/gitlab/utils/usage_data_spec.rb

@@ -183,6 +183,24 @@
     end
   end
 
+  describe '#add' do
+    it 'adds given values' do
+      expect(described_class.add(1, 3)).to eq(4)
+    end
+
+    it 'adds given values' do
+      expect(described_class.add).to eq(0)
+    end
+
+    it 'returns the fallback value when adding fails' do
+      expect(described_class.add(nil, 3)).to eq(-1)
+    end
+
+    it 'returns the fallback value one of the arguments is negative' do
+      expect(described_class.add(-1, 1)).to eq(-1)
+    end
+  end
+
   describe '#alt_usage_data' do
     it 'returns the fallback when it gets an error' do
       expect(described_class.alt_usage_data { raise StandardError } ).to eq(-1)