Lateral expressions for PostgreSQL

lib/arel/nodes/select_core.rb

@@ -10,7 +10,7 @@ def initialize
         @source         = JoinSource.new nil
         @top            = nil
 
-        # http://savage.net.au/SQL/sql-92.bnf.html#set%20quantifier
+        # https://ronsavage.github.io/SQL/sql-92.bnf.html#set%20quantifier
         @set_quantifier = nil
         @projections    = []
         @wheres         = []

lib/arel/nodes/unary.rb

@@ -28,6 +28,7 @@ def eql? other
       Group
       GroupingElement
       GroupingSet
+      Lateral
       Limit
       Lock
       Not

lib/arel/select_manager.rb

@@ -204,6 +204,11 @@ def except other
     end
     alias :minus :except
 
+    def lateral table_name = nil
+      base = table_name.nil? ? ast : as(table_name)
+      Nodes::Lateral.new(base)
+    end
+
     def with *subqueries
       if subqueries.first.is_a? Symbol
         node_class = Nodes.const_get("With#{subqueries.shift.to_s.capitalize}")

lib/arel/visitors/depth_first.rb

@@ -25,6 +25,7 @@ def unary o
       alias :visit_Arel_Nodes_GroupingElement   :unary
       alias :visit_Arel_Nodes_Grouping          :unary
       alias :visit_Arel_Nodes_Having            :unary
+      alias :visit_Arel_Nodes_Lateral           :unary
       alias :visit_Arel_Nodes_Limit             :unary
       alias :visit_Arel_Nodes_Not               :unary
       alias :visit_Arel_Nodes_Offset            :unary

lib/arel/visitors/postgresql.rb

@@ -5,6 +5,7 @@ class PostgreSQL < Arel::Visitors::ToSql
       CUBE = 'CUBE'
       ROLLUP = 'ROLLUP'
       GROUPING_SET = 'GROUPING SET'
+      LATERAL = 'LATERAL'
 
       private
 
@@ -69,6 +70,23 @@ def visit_Arel_Nodes_GroupingSet o, collector
         grouping_array_or_grouping_element o, collector
       end
 
+      def visit_Arel_Nodes_Lateral o, collector
+        collector << LATERAL
+        collector << SPACE
+        grouping_parentheses o, collector
+      end
+
+      # Used by Lateral visitor to enclose select queries in parentheses
+      def grouping_parentheses o, collector
+        if o.expr.is_a? Nodes::SelectStatement
+          collector << "("
+          visit o.expr, collector
+          collector << ")"
+        else
+          visit o.expr, collector
+        end
+      end
+
       # Utilized by GroupingSet, Cube & RollUp visitors to
       # handle grouping aggregation semantics
       def grouping_array_or_grouping_element o, collector

test/visitors/test_postgres.rb

@@ -51,6 +51,20 @@ def compile node
         assert_equal 'SELECT DISTINCT', compile(core)
       end
 
+      it 'encloses LATERAL queries in parens' do
+        subquery = @table.project(:id).where(@table[:name].matches('foo%'))
+        compile(subquery.lateral).must_be_like %{
+          LATERAL (SELECT id FROM "users" WHERE "users"."name" ILIKE 'foo%')
+        }
+      end
+
+      it 'produces LATERAL queries with alias' do
+        subquery = @table.project(:id).where(@table[:name].matches('foo%'))
+        compile(subquery.lateral('bar')).must_be_like %{
+          LATERAL (SELECT id FROM "users" WHERE "users"."name" ILIKE 'foo%') bar
+        }
+      end
+
       describe "Nodes::Matches" do
         it "should know how to visit" do
           node = @table[:name].matches('foo%')