Add Fizzbuzz With Common Table Expressions as a postgres til.

postgres/fizzbuzz-with-common-table-expressions.md

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+# Fizzbuzz With Common Table Expressions
+
+In learning about CTEs (common table expressions) in postgres, I discovered
+that you can do some interesting and powerful things using the `with
+recursive` construct. The following solves the fizzbuzz problem for integers
+up to 100
+
+```sql
+with recursive fizzbuzz (num,val) as (
+    select 0, ''
+    union
+    select (num + 1),
+      case
+      when (num + 1) % 15 = 0 then 'fizzbuzz'
+      when (num + 1) % 5  = 0 then 'buzz'
+      when (num + 1) % 3  = 0 then 'fizz'
+      else (num + 1)::text
+      end
+    from fizzbuzz
+    where num < 100
+)
+select val from fizzbuzz where num > 0;
+```