Add Generate A UUID as a postgres til.

README.md

@@ -108,6 +108,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Edit Existing Functions](postgres/edit-existing-functions.md)
 - [Extracting Nested JSON Data](postgres/extracting-nested-json-data.md)
 - [Fizzbuzz With Common Table Expressions](postgres/fizzbuzz-with-common-table-expressions.md)
+- [Generate A UUID](postgres/generate-a-uuid.md)
 - [Generate Series Of Numbers](postgres/generate-series-of-numbers.md)
 - [Getting A Slice Of An Array](postgres/getting-a-slice-of-an-array.md)
 - [Integers In Postgres](postgres/integers-in-postgres.md)

postgres/generate-a-uuid.md

@@ -0,0 +1,19 @@
+# Generate A UUID
+
+Postgres has support for universally unique identifiers (UUIDs) as a column
+data type via `uuid`. If you have a UUID column, you may need to generate a
+UUID.  This requires the `uuid-ossp` module. This module provides a number
+of functions for generating UUIDs including the `uuid_generate_v4()`
+function which bases the UUID entirely off random numbers.
+
+```sql
+> create extension "uuid-ossp";
+CREATE EXTENSION
+> select uuid_generate_v4();
+           uuid_generate_v4
+--------------------------------------
+ a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11
+```
+
+See the [postgres docs](http://www.postgresql.org/docs/9.4/static/uuid-ossp.html) for more
+details on UUID generation functions.