Dynamic Query in sql server

Create table #info (id int,Sname varchar(50))
Create table #Post (Post_id int, id int,post varchar(50))
Create table #city (city_id int,id int,city varchar(100))

   insert into #info(id,Sname) values(1,'sandip.')
   insert into #info(id,Sname) values(2,'sandip_SP')
   insert into #info(id,Sname) values(3,'sandip_Ak')
   insert into #info(id,Sname) values(4,'sandip_Sk')
   insert into #info(id,Sname) values(5,'sandipG')
   insert into #Post(Post_id ,id,post) values(1,1,'Software Dev')
   insert into #Post(Post_id ,id,post) values(2,2,'Database admin')
   insert into #Post(Post_id ,id,post) values(3,3,'tester')
   insert into #Post(Post_id ,id,post) values(4,4,'HR')
   insert into #Post(Post_id ,id,post) values(5,5,'Team Lead')
   insert into #city (city_id,id,city) values (1,1,'kolhapur')
   insert into #city (city_id,id,city) values (1,1,'sangli')
   insert into #city (city_id,id,city) values (1,1,'satara')
   insert into #city (city_id,id,city) values (1,1,'karad')
   insert into #city (city_id,id,city) values (1,1,'maharastra')

     declare @main_str varchar(max)
     declare @query_str varchar(max)
     declare @InnerJoin_str varchar(max)
     declare @Where_str varchar(max)
     set @query_str =' select * from #temp a ' 
     set @InnerJoin_str =' inner join #post b on a.id=b.id '
     set @Where_str= 'Where a.id=4 '
     set @main_str=''
     set @main_str=@query_str+@InnerJoin_str+@Where_str
     exec(@main_str)
    --Add Dynamacally where clause in sql query
    set @Where_str=@Where_str+ ' or b.post=''Software Dev'''
    set @main_str=''
    set @main_str=@query_str+@InnerJoin_str+@Where_str
    exec(@main_str)
 --Add Dynamacally joins in sql Query
   set @InnerJoin_str=@InnerJoin_str+ ' inner join #city c on a.id=c.id '
   set @main_str=''
   set @main_str=@query_str+@InnerJoin_str+@Where_str
   exec(@main_str)

  link:http://sandipgsql.blogspot.in/2013/05/dynamic-query-in-sql-server.html