diff --git a/04-databases/basic-sql-blog/Main.m b/04-databases/basic-sql-blog/Main.m
index bcd0ed9..dc981c7 100644
--- a/04-databases/basic-sql-blog/Main.m
+++ b/04-databases/basic-sql-blog/Main.m
@@ -1,4 +1,5 @@
 
+  zlink "routines/Category"
   zlink "routines/Comment"
   zlink "routines/Database"
   zlink "routines/Post"
@@ -9,22 +10,49 @@
   s ok=$$set^User(1,"alice~password~alice-jones@no-reply.com~Alice Jones")
   s ok=$$set^User(2,"bob~password~bob-smith@no-reply.com~Bob Smith")
 
-; create posts
+; create categories
 
-  s ok=$$set^Post(1,1,"lorem-ipsum~Lorem ipsum~Lorem ipsum dolor sit amet, consectetuer adipiscing elit.")
-  s ok=$$set^Post(2,1,"donec-pede-justo~Donec pede justo~Donec pede justo, fringilla vel, aliquet nec, vulputate eget, arcu.")
-  s ok=$$set^Post(3,2,"curabitur-ullamcorper-ultricies~Curabitur ullamcorper ultricies~ Curabitur ullamcorper ultricies nisi.")
-  s ok=$$set^Post(4,2,"donec-vitae-sapien~Donec vitae sapien~Donec vitae sapien ut libero venenatis faucibus. Nullam quis ante.")
+  s ok=$$set^Category(1,"foo~Foo")
+  s ok=$$set^Category(2,"bar~Bar")
+  s ok=$$set^Category(3,"foobar~Foobar")
+
+; create posts
+;
+; s ok=$$set^Post(1, ...
+;                 ⮡ post id
+; s ok=$$set^Post(1,1, ...
+;                   ⮡ category id
+; s ok=$$set^Post(1,1,1 ...
+;                     ⮡ user id
+
+  s ok=$$set^Post(1,1,1,"lorem-ipsum~Lorem ipsum~Lorem ipsum dolor sit amet, consectetuer adipiscing elit.")
+  s ok=$$set^Post(2,1,1,"donec-pede-justo~Donec pede justo~Donec pede justo, fringilla vel, aliquet nec, vulputate eget, arcu.")
+  s ok=$$set^Post(3,3,2,"curabitur-ullamcorper-ultricies~Curabitur ullamcorper ultricies~ Curabitur ullamcorper ultricies nisi.")
+  s ok=$$set^Post(4,3,2,"donec-vitae-sapien~Donec vitae sapien~Donec vitae sapien ut libero venenatis faucibus. Nullam quis ante.")
 
 ; create comments
 
   s ok=$$set^Comment(1,1,"This is awesome! Thank you.")
   s ok=$$set^Comment(2,2,"Thank you so much for sharing this.")
 
+; fetch categories
+
+  do fetch^Category(1,.data)
+  w "Category fetched:",!
+  w "description: ",data("description"),!
+
+  do fetch^Category(2,.data)
+  w !,"Category fetched:",!
+  w "description: ",data("description"),!
+
+  do fetch^Category(3,.data)
+  w !,"Category fetched:",!
+  w "description: ",data("description"),!
+
 ; fetch posts by post
 
   do fetch^Post(1,.data)
-  w "Post fetched:",!
+  w !,"Post fetched:",!
   w "slug: ",data("slug"),!
   w "title: ",data("title"),!
   w "description: ",data("description"),!
@@ -39,8 +67,15 @@
 
   do fetchByUser^Post(1,.data)
   w !,"Posts fetched by user:",!
-  w data(1),!
-  w data(2),!
+  s lev1=""
+  f  s lev1=$o(data(lev1)) q:lev1=""  d  w data(lev1),!
+
+; fetch posts by category
+
+  do fetchByCategory^Post(3,.data)
+  w !,"Posts fetched by category:",!
+  s lev1=""
+  f  s lev1=$o(data(lev1)) q:lev1=""  d  w data(lev1),!
 
 ; fetch comments
 
diff --git a/04-databases/basic-sql-blog/routines/Category.m b/04-databases/basic-sql-blog/routines/Category.m
new file mode 100644
index 0000000..fb36c5d
--- /dev/null
+++ b/04-databases/basic-sql-blog/routines/Category.m
@@ -0,0 +1,21 @@
+
+fetch(id,data)
+  n record
+  k data
+  i id="" q 0
+  s record=$get(^categories(id))
+  s data("slug")=$piece(record,"~",1)
+  s data("description")=$piece(record,"~",2)
+  q
+
+set(id,data)
+  i id="" q 0
+  s slug=$piece(data,"~",1)
+  s description=$piece(data,"~",2)
+  s ^categories(id)=slug_"~"_description
+  q 1
+
+remove(id)
+  i id="" q 0
+  k ^categories(id)
+  q 1
diff --git a/04-databases/basic-sql-blog/routines/Database.m b/04-databases/basic-sql-blog/routines/Database.m
index b10163c..cb7a45f 100644
--- a/04-databases/basic-sql-blog/routines/Database.m
+++ b/04-databases/basic-sql-blog/routines/Database.m
@@ -2,5 +2,6 @@
 drop()
   k ^comments;
   k ^posts;
+  k ^categories;
   k ^users;
   q 1
diff --git a/04-databases/basic-sql-blog/routines/Post.m b/04-databases/basic-sql-blog/routines/Post.m
index ee0efc9..1f645ed 100644
--- a/04-databases/basic-sql-blog/routines/Post.m
+++ b/04-databases/basic-sql-blog/routines/Post.m
@@ -5,14 +5,31 @@ fetch(id,data)
   i id="" q 0
   s lev1=""
   s lev2=""
+  s lev3=""
   f  s lev1=$o(^posts(lev1)) q:lev1=""  d
   . f  s lev2=$o(^posts(lev1,lev2)) q:lev2=""  d
-  . . i lev1=id d
-  . . . s record=$get(^posts(id,lev2))
-  . . . s data("slug")=$piece(record,"~",1)
-  . . . s data("title")=$piece(record,"~",2)
-  . . . s data("description")=$piece(record,"~",3)
-  . . . q
+  . . f  s lev3=$o(^posts(lev1,lev2,lev3)) q:lev3=""  d
+  . . . i lev1=id d
+  . . . . s record=$get(^posts(lev1,lev2,lev3))
+  . . . . s data("slug")=$piece(record,"~",1)
+  . . . . s data("title")=$piece(record,"~",2)
+  . . . . s data("description")=$piece(record,"~",3)
+  . . . . q
+  q
+
+fetchByCategory(idCategory,data)
+  k data
+  i idCategory="" q 0
+  s lev1=""
+  s lev2=""
+  s lev3=""
+  s count=1
+  f  s lev1=$o(^posts(lev1)) q:lev1=""  d
+  . f  s lev2=$o(^posts(lev1,lev2)) q:lev2=""  d
+  . . f  s lev3=$o(^posts(lev1,lev2,lev3)) q:lev3=""  d
+  . . . i lev2=idCategory d
+  . . . . s data(count)=$get(^posts(lev1,lev2,lev3))
+  . . . . s count=count+1
   q
 
 fetchByUser(idUser,data)
@@ -20,20 +37,22 @@ fetchByUser(idUser,data)
   i idUser="" q 0
   s lev1=""
   s lev2=""
+  s lev3=""
   s count=1
   f  s lev1=$o(^posts(lev1)) q:lev1=""  d
   . f  s lev2=$o(^posts(lev1,lev2)) q:lev2=""  d
-  . . i lev2=idUser d
-  . . . s data(count)=$get(^posts(lev1,idUser))
-  . . . s count=count+1
+  . . f  s lev3=$o(^posts(lev1,lev2,lev3)) q:lev3=""  d
+  . . . i lev3=idUser d
+  . . . . s data(count)=$get(^posts(lev1,lev2,lev3))
+  . . . . s count=count+1
   q
 
-set(id,idUser,data)
-  i id=""!idUser="" q 0
+set(id,idCategory,idUser,data)
+  i id=""!idCategory=""!idUser="" q 0
   s slug=$piece(data,"~",1)
   s title=$piece(data,"~",2)
   s description=$piece(data,"~",3)
-  s ^posts(id,idUser)=slug_"~"_title_"~"_description
+  s ^posts(id,idCategory,idUser)=slug_"~"_title_"~"_description
   q 1
 
 remove(id)