Optimization regarding lesson control. Dropped a redundant column in …

…chapters table, as we can query the max sec in sqlcons table.

app/controllers/home_controller.rb

@@ -15,7 +15,7 @@ def index
   def jump_to_lesson
 	chapter = params[:id]
 	#Initialize session variables before we direct to that chapter
-  	session[:maxsec]  = Chapters.select(:maxlesson).where("id = #{chapter}").first.maxlesson	
+  	session[:maxsec]  = Sqlcons.maximum(:sec, :conditions => "ch = #{chapter}")#.where("ch = #{chapter}")	
   	session[:maxch]   = Chapters.maximum(:id)
   	session[:tutch]   = chapter.to_i 
 	session[:tutsec]  = 0 

app/controllers/sqlcons_controller.rb

@@ -6,13 +6,10 @@ class SqlconsController < ApplicationController
   # GET /sqlcons
   # GET /sqlcons.json
   def index
-  	session[:maxsec]  = Chapters.select(:maxlesson).where("id = 1").first.maxlesson	
+  	session[:maxsec]  = Sqlcons.maximum(:sec).where("ch = 1")	
+  	#session[:maxsec]  = Chapters.select(:maxlesson).where("id = 1").first.maxlesson	
   	session[:tutch]   = 1
-    session[:tutsec]  = 1  
-  	#respond_to do |format|
-     #   format.html # index.html.erb
-     #   format.json { render :json => @sqlcons }
-     # end
+    	session[:tutsec]  = 1  
 	render :index  
   end
 
@@ -42,7 +39,8 @@ def fetchquery
 
   #Increments session parameters if user wants to advance lesson.
   def nextlesson
-	cur_sec_max = Chapters.select(:maxlesson).where(:id => session[:tutch]).first.maxlesson
+	cur_sec_max = Sqlcons.maximum(:sec, :conditions => "ch = " + session[:tutch].to_s)
+	#Chapters.select(:maxlesson).where(:id => session[:tutch]).first.maxlesson
 	app_ch_max = Chapters.maximum("id")
 	#If we haven't hit the last lesson in chapter, or last chapter of tutorial
 	# increment lesson. Otherwise on to the next chapter

app/views/sqlcons/tutorials/tut4-2.html

@@ -0,0 +1,9 @@
+<h3>Ch4-2 : Count (cont.)</h3>
+<p>
+To further assist in data analysis, we can employ the <code>group by<code> clause. 
+<br /> <br />
+This addition allows us to "group" aggregate function results together based on values in a column. 
+<br /><code>select count(*) from students</code>
+<br /><code>select count(*) from students where fname like 'S%'</code>
+<br / > 
+</p>

db/migrate/20120508230755_dropmaxlesson_from_chapters.rb

@@ -0,0 +1,8 @@
+class DropmaxlessonFromChapters < ActiveRecord::Migration
+  def up
+  	remove_column :chapters, :maxlesson
+  end
+
+  def down
+  end
+end

db/schema.rb

@@ -11,14 +11,13 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20120414223318) do
+ActiveRecord::Schema.define(:version => 20120508230755) do
 
   create_table "chapters", :force => true do |t|
     t.string   "title"
     t.datetime "created_at",  :null => false
     t.datetime "updated_at",  :null => false
     t.string   "description"
-    t.integer  "maxlesson"
   end
 
   create_table "dbqs", :force => true do |t|

db/seeds.rb

@@ -25,6 +25,10 @@
 
 #Chapter 4
 Sqlcons.create(ch: 4,sec: 1,regtext: '(select)(.*?)(count)');
+Sqlcons.create(ch: 4,sec: 2,regtext: '(select)(.*?)(group by)');
+Sqlcons.create(ch: 4,sec: 3,regtext: '(select)(.*?)(having)');
+Sqlcons.create(ch: 4,sec: 4,regtext: '(select)(.*?)(max|min)');
+Sqlcons.create(ch: 4,sec: 5,regtext: '(select)(.*?)(sum)');
 
 #Chapter description for each chapter.
 Chapters.create( title:'Select' , description:'The most basic forms of querying a database', maxlesson:7);