Added LEFT JOIN.

Author: Dray Lacy

lib/sql/parser.racc

@@ -38,7 +38,11 @@ rule
     | table_reference CROSS JOIN table_name { result = SQL::Statement::CrossJoin.new(val[0], SQL::Statement::Table.new(val[3])) }
 
   qualified_join
-    : table_reference INNER JOIN table_reference join_specification { result = SQL::Statement::InnerJoin.new(val[0], val[3], val[4]) }
+    : table_reference join_type JOIN table_reference join_specification { result = val[1].new(val[0], val[3], val[4]) }
+
+  join_type
+    : INNER { result = SQL::Statement::InnerJoin }
+    | LEFT { result = SQL::Statement::LeftJoin }
 
   join_specification
     : join_condition

lib/sql/parser.racc.rb

@@ -53,6 +53,7 @@ rule
             CROSS       { [:CROSS, text] }
             JOIN        { [:JOIN, text] }
             ON          { [:ON, text] }
+            LEFT        { [:LEFT, text] }
 
 # tokens
             <>          { [:not_equals_operator, text] }

lib/sql/parser.rex

@@ -146,6 +146,9 @@ def scan_evaluate( str )
         when (text = ss.scan(/ON/))
            @rex_tokens.push action { [:ON, text] }
 
+        when (text = ss.scan(/LEFT/))
+           @rex_tokens.push action { [:LEFT, text] }
+
         when (text = ss.scan(/<>/))
            @rex_tokens.push action { [:not_equals_operator, text] }
 

lib/sql/parser.rex.rb

@@ -153,6 +153,10 @@ def visit_InnerJoin(o)
       "#{visit(o.left)} INNER JOIN #{visit(o.right)} ON #{visit(o.search_condition)}"
     end
 
+    def visit_LeftJoin(o)
+      "#{visit(o.left)} LEFT JOIN #{visit(o.right)} ON #{visit(o.search_condition)}"
+    end
+
     def visit_Table(o)
       o.name
     end

lib/sql/sql_visitor.rb

@@ -233,6 +233,9 @@ def initialize(left, right, search_condition)
     class InnerJoin < QualifiedJoin
     end
 
+    class LeftJoin < QualifiedJoin
+    end
+
     class Table < Node
       def initialize(name)
         @name = name

lib/sql/statement.rb

@@ -2,6 +2,11 @@
 require 'test/unit'
 
 class TestParser < Test::Unit::TestCase
+  def test_left_join
+    assert_understands 'SELECT * FROM t1 LEFT JOIN t2 ON t1.a = t2.a'
+    assert_understands 'SELECT * FROM t1 LEFT JOIN t2 ON t1.a = t2.a LEFT JOIN t3 ON t2.a = t3.a'
+  end
+
   def test_inner_join
     assert_understands 'SELECT * FROM t1 INNER JOIN t2 ON t1.a = t2.a'
     assert_understands 'SELECT * FROM t1 INNER JOIN t2 ON t1.a = t2.a INNER JOIN t3 ON t2.a = t3.a'

test/test_parser.rb

@@ -28,6 +28,10 @@ def test_from_clause
     assert_sql 'FROM users', SQL::Statement::FromClause.new(SQL::Statement::Table.new('users'))
   end
 
+  def test_left_join
+    assert_sql 't1 LEFT JOIN t2 ON t1.a = t2.a', SQL::Statement::LeftJoin.new(SQL::Statement::Table.new('t1'), SQL::Statement::Table.new('t2'), SQL::Statement::Equals.new(SQL::Statement::QualifiedColumn.new('t1', 'a'), SQL::Statement::QualifiedColumn.new('t2', 'a')))
+  end
+
   def test_inner_join
     assert_sql 't1 INNER JOIN t2 ON t1.a = t2.a', SQL::Statement::InnerJoin.new(SQL::Statement::Table.new('t1'), SQL::Statement::Table.new('t2'), SQL::Statement::Equals.new(SQL::Statement::QualifiedColumn.new('t1', 'a'), SQL::Statement::QualifiedColumn.new('t2', 'a')))
   end