adding support for subqueries

lib/dialect/postgres.js

@@ -10,9 +10,11 @@ Postgres.prototype.getQuery = function(queryNode) {
   return { text: this.output.join(' '), values: this.params };
 }
 
+
 Postgres.prototype.visit = function(node) {
   switch(node.type) {
     case 'QUERY': return this.visitQuery(node);
+    case 'SUBQUERY': return this.visitSubquery(node);
     case 'SELECT': return this.visitSelect(node);
     case 'INSERT': return this.visitInsert(node);
     case 'UPDATE': return this.visitUpdate(node);
@@ -136,6 +138,24 @@ Postgres.prototype.visitQuery = function(queryNode) {
   return this;
 }
 
+Postgres.prototype.visitSubquery = function(queryNode) {
+  var result = [];
+  for(var i = 0; i < queryNode.nodes.length; i ++) {
+    var res = this.visit(queryNode.nodes[i]);
+    result = result.concat(res);
+  }
+  //implicit 'from'
+  if(!this._visitedFrom) {
+    var select = result.slice(0, this._selectOrDeleteEndIndex);
+    var from = this.visitFrom(new From().add(queryNode.table.toNode()));
+    var rest = result.slice(this._selectOrDeleteEndIndex);
+    result = select.concat(from).concat(rest);
+  }
+  result[0] = '('+result[0];
+  result[result.length-1] = result[result.length-1] + ') ' + queryNode.alias;
+  return result;
+}
+
 Postgres.prototype.visitTable = function(tableNode) {
   var table = tableNode.table;
   var txt="";

lib/table.js

@@ -54,6 +54,14 @@ Table.prototype.select = function() {
   return query;
 }
 
+Table.prototype.subQuery = function(alias) {
+  //create the query and pass it off
+  var query = new Query(this);
+  query.type = 'SUBQUERY';
+  query.alias = alias;
+  return query;
+}
+
 Table.prototype.insert = function() {
   var query = new Query(this);
   query.insert.apply(query, arguments);

test/dialect-tests.js

@@ -97,6 +97,23 @@ test({
   pg    : 'SELECT "user"."name", "post"."content" FROM "user" INNER JOIN "post" ON ("user"."id" = "post"."userId")'
 });
 
+test({
+  query : user
+    .select(user.name, post.content)
+    .from(user.join(
+      post
+        .subQuery('subposts')
+        .select(post.content, post.userId)
+        .from(post))
+    .on(user.id.equals(post.userId))),
+  pg    : 'SELECT "user"."name", "post"."content" FROM "user" INNER JOIN (SELECT "post"."content", "post"."userId" FROM "post") subposts ON ("user"."id" = "post"."userId")'
+});
+
+test({
+  query : user.select(user.name.as('user name'), user.id.as('user id')).from(user),
+  pg    : 'SELECT "user"."name" as "user name", "user"."id" as "user id" FROM "user"'
+});
+
 test({
   query : user.select(user.name.as('user name')).from(user).where(user.name.equals('brian')),
   pg    : 'SELECT "user"."name" as "user name" FROM "user" WHERE ("user"."name" = $1)'