Add Special Math Operators as a postgres til.

postgres/special-math-operators.md

@@ -0,0 +1,35 @@
+# Special Math Operators
+
+Postgres has all the mathematical operators you might expect in any
+programming language (e.g. `+`,`-`,`*`,`/`,`%`). It also has a few extras
+that you might not be expecting.
+
+Factorial Operator:
+
+```sql
+> select 5!;
+ ?column?
+----------
+      120
+(1 row)
+```
+
+Square Root Operator:
+
+```sql
+> select |/81;
+ ?column?
+----------
+        9
+(1 row)
+```
+
+Absolute Value Operator:
+
+```sql
+> select @ -23.4;
+ ?column?
+----------
+     23.4
+(1 row)
+```