Add Types By Category as a postgres til.

README.md

@@ -93,6 +93,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Timestamp Functions](postgres/timestamp-functions.md)
 - [Toggling The Pager In PSQL](postgres/toggling-the-pager-in-psql.md)
 - [Turning Timing On](postgres/turning-timing-on.md)
+- [Types By Category](postgres/types-by-category.md)
 - [Use Argument Indexes](postgres/use-argument-indexes.md)
 - [Using Intervals To Offset Time](postgres/using-intervals-to-offset-time.md)
 - [Who Is The Current User](postgres/who-is-the-current-user.md)

postgres/types-by-category.md

@@ -0,0 +1,35 @@
+# Types By Category
+
+Postgres has many types, each of which fall into a particular category.
+These categories include Array, Boolean, String, Numeric, Composite, etc.
+Each of these categories has a corresponding code. For instance, numeric
+types have a code of `N`. Using `N` I can get a list of all the numeric
+types:
+
+```sql
+> select typname from pg_type where typcategory = 'N';
+     typname
+-----------------
+ int8
+ int2
+ int4
+ regproc
+ oid
+ float4
+ float8
+ money
+ numeric
+ regprocedure
+ regoper
+ regoperator
+ regclass
+ regtype
+ regconfig
+ regdictionary
+ cardinal_number
+(17 rows)
+```
+
+Check out
+[`pg_type`](http://www.postgresql.org/docs/current/interactive/catalog-pg-type.html)
+in the Postgres docs for a list of all categories and codes.