diff --git a/lib/query.js b/lib/query.js
index 051a565..11037fb 100644
--- a/lib/query.js
+++ b/lib/query.js
@@ -6,12 +6,12 @@ var SqlTree = require('./sqltree');
 var type = require('./type');
 var inflection = require('./inflection');
 
-var Query = function (connection, model) {
+var Query = function(connection, model) {
   var self = this;
-  this._getConnection = function () { return connection; }; // hide from JSON.stringify
+  this._getConnection = function() { return connection; }; // hide from JSON.stringify
   this.model = model;
   var tableIndex = 0;
-  this._getNextTableAlias = function () { return 't' + (tableIndex++); };
+  this._getNextTableAlias = function() { return 't' + (tableIndex++); };
   this.count = persistUtil.bind('count', this.count, this);
   this.all = persistUtil.bind('all', this.all, this);
   this.first = persistUtil.bind('first', this.first, this);
@@ -22,7 +22,7 @@ var Query = function (connection, model) {
   this.max = persistUtil.bind('max', this.max, this);
 
   var sqlTree = new SqlTree(model);
-  this._sqlTree = function () { return sqlTree; }; // hide from JSON.stringify
+  this._sqlTree = function() { return sqlTree; }; // hide from JSON.stringify
 
   sqlTree.tableAlias = this._getNextTableAlias();
   if (model.columns) {
@@ -40,7 +40,7 @@ var Query = function (connection, model) {
 // "name = ? AND age = ?", ["bob", 6]
 // "name = 'bob'"
 // { "name": "bob", "age", 6 }
-Query.prototype.where = function () {
+Query.prototype.where = function() {
   if (typeof (arguments[0]) === 'string') {
     var expr = arguments[0];
     var params = Array.prototype.slice.call(arguments, 1);
@@ -63,12 +63,11 @@ Query.prototype.whereIn = function() {
     var expr = arguments[0];
     var params = arguments[1];
     var paramCount = params.length;
-    expr =  expr + ' IN (';
+    expr = expr + ' IN (';
     var i;
-      for(i = 0; i < paramCount-1; i++)
-      {
-        expr = expr + "?,"
-      }
+    for (i = 0; i < paramCount - 1; i++) {
+      expr = expr + "?,"
+    }
     expr = expr + '?)'
     this.where(expr, params);
   }
@@ -80,7 +79,7 @@ Query.prototype.whereIn = function() {
 
 // "people"
 // ["people", "phones"]
-Query.prototype.include = function () {
+Query.prototype.include = function() {
   var join;
   if (typeof (arguments[0]) === 'string') {
     var associationPropertyName = arguments[0];
@@ -130,20 +129,20 @@ Query.prototype.include = function () {
   return this;
 };
 
-Query.prototype.join = function (otherTable, otherTableId, thisTableId) {
+Query.prototype.join = function(otherTable, otherTableId, thisTableId) {
   return this._join.apply(this, ['join'].concat(persistUtil.toArray(arguments)));
 };
 
-Query.prototype.leftJoin = function (otherTable, otherTableId, thisTableId) {
+Query.prototype.leftJoin = function(otherTable, otherTableId, thisTableId) {
   return this._join.apply(this, ['left join'].concat(persistUtil.toArray(arguments)));
 };
 
 // type, otherTable, otherTableId, thisTableId
 // type, associationPropertyName
-Query.prototype._join = function (type, otherTable, otherTableId, thisTableId) {
+Query.prototype._join = function(type, otherTable, otherTableId, thisTableId) {
   if (arguments.length === 2) {
     var association = this.model.associations[arguments[1]]
-      || this.model.associations[inflection.singularize(arguments[1])]
+                        || this.model.associations[inflection.singularize(arguments[1])]
       || this.model.associations[inflection.pluralize(arguments[1])];
     otherTable = association.model.tableName;
     if (association.type === 'hasOne') {
@@ -171,7 +170,7 @@ Query.prototype._join = function (type, otherTable, otherTableId, thisTableId) {
   return this;
 };
 
-Query.prototype.orderBy = function (name, orderByDirection) {
+Query.prototype.orderBy = function(name, orderByDirection) {
   var column = this._sqlTree().getColumnByPropertyName(name);
   if (column === null) {
     throw new Error("Invalid property name [" + name + "] for order by clause.");
@@ -180,7 +179,7 @@ Query.prototype.orderBy = function (name, orderByDirection) {
   return this;
 };
 
-Query.prototype.limit = function (count, offset) {
+Query.prototype.limit = function(count, offset) {
   this._sqlTree().limitCount = count;
   this._sqlTree().limitOffset = offset;
   return this;
@@ -188,7 +187,7 @@ Query.prototype.limit = function (count, offset) {
 
 // connection, callback, doneCallback
 // callback, doneCallback
-Query.prototype.each = function () {
+Query.prototype.each = function() {
   var connection = this._getConnection();
   if (arguments[0] instanceof Connection) {
     connection = arguments[0];
@@ -206,7 +205,7 @@ Query.prototype.each = function () {
   connection.each(this._sqlTree(), callback, doneCallback);
 };
 
-Query.prototype.count = function () {
+Query.prototype.count = function() {
   var connection = this._getConnection();
   if (arguments[0] instanceof Connection) {
     connection = arguments[0];
@@ -223,11 +222,11 @@ Query.prototype.count = function () {
 // field (chaining)
 // connection, field, callback
 // field, callback
-Query.prototype.min = function () {
+Query.prototype.min = function() {
   var self = this;
   if (arguments.length === 1) {
     var fieldName = arguments[0];
-    return function (connection, callback) {
+    return function(connection, callback) {
       self.min(connection, fieldName, callback);
     };
   }
@@ -251,11 +250,11 @@ Query.prototype.min = function () {
 // field (chaining)
 // connection, field, callback
 // field, callback
-Query.prototype.max = function () {
+Query.prototype.max = function() {
   var self = this;
   if (arguments.length === 1) {
     var fieldName = arguments[0];
-    return function (connection, callback) {
+    return function(connection, callback) {
       self.max(connection, fieldName, callback);
     };
   }
@@ -279,11 +278,11 @@ Query.prototype.max = function () {
 // field (chaining)
 // connection, field, callback
 // field, callback
-Query.prototype.sum = function () {
+Query.prototype.sum = function() {
   var self = this;
   if (arguments.length === 1) {
     var fieldName = arguments[0];
-    return function (connection, callback) {
+    return function(connection, callback) {
       self.sum(connection, fieldName, callback);
     };
   }
@@ -300,11 +299,19 @@ Query.prototype.sum = function () {
 
   this._sqlTree().action = 'sum';
   this._sqlTree().columns = [ this._sqlTree().getColumnByPropertyName(field) ];
-  connection.single(this._sqlTree(), 'sum', callback);
+  connection.single(this._sqlTree(), 'sum', function(err, sum) {
+    if (err) {
+      return callback(err);
+    }
+    if (sum === null) {
+      sum = 0;
+    }
+    return callback(null, sum);
+  });
   return null;
 };
 
-Query.prototype.all = function () {
+Query.prototype.all = function() {
   var connection = this._getConnection();
   if (arguments[0] instanceof Connection) {
     connection = arguments[0];
@@ -317,7 +324,7 @@ Query.prototype.all = function () {
   connection.all(this._sqlTree(), callback);
 };
 
-Query.prototype.first = function () {
+Query.prototype.first = function() {
   var connection = this._getConnection();
   if (arguments[0] instanceof Connection) {
     connection = arguments[0];
@@ -332,7 +339,7 @@ Query.prototype.first = function () {
   if (this._sqlTree().includes.length === 0) {
     this.limit(1);
   }
-  this.all(connection, function (err, rows) {
+  this.all(connection, function(err, rows) {
     if (err) {
       callback(err);
       return;
@@ -345,7 +352,7 @@ Query.prototype.first = function () {
   });
 };
 
-Query.prototype.last = function () {
+Query.prototype.last = function() {
   var connection = this._getConnection();
   if (arguments[0] instanceof Connection) {
     connection = arguments[0];
@@ -355,21 +362,21 @@ Query.prototype.last = function () {
   }
   var callback = arguments[arguments.length - 1];
 
-  this.all(connection, function (err, rows) {
+  this.all(connection, function(err, rows) {
     if (err) {
       callback(err);
-     return;
-   }
-   if (rows.length === 0) {
-     callback(null, null);
-   } else {
-     callback(null, rows[rows.length-1]);
+      return;
+    }
+    if (rows.length === 0) {
+      callback(null, null);
+    } else {
+      callback(null, rows[rows.length - 1]);
     }
   });
 };
 
 
-Query.prototype.getById = function () {
+Query.prototype.getById = function() {
   var args = persistUtil.toArray(arguments);
   var connection = this._getConnection();
   if (args[0] instanceof Connection) {
@@ -382,7 +389,7 @@ Query.prototype.getById = function () {
   var id = args[0];
   var callback = args[args.length - 1];
 
-  this.where(this.model.getIdPropertyName() + " = ?", id).first(connection, function (err, row) {
+  this.where(this.model.getIdPropertyName() + " = ?", id).first(connection, function(err, row) {
     if (err) {
       callback(err);
       return;
@@ -391,7 +398,7 @@ Query.prototype.getById = function () {
   });
 };
 
-Query.prototype.deleteAll = function () {
+Query.prototype.deleteAll = function() {
   var connection = this._getConnection();
   if (arguments[0] instanceof Connection) {
     connection = arguments[0];
@@ -406,7 +413,7 @@ Query.prototype.deleteAll = function () {
   this.all(connection, callback);
 };
 
-Query.prototype.updateAll = function () {
+Query.prototype.updateAll = function() {
   var connection = this._getConnection();
   if (arguments[0] instanceof Connection) {
     connection = arguments[0];