Add Generating UUIDs With pgcrypto as a postgres til

Author: jbranchaud

README.md

@@ -7,7 +7,7 @@ variety of languages and technologies. These are things that don't really
 warrant a full blog post. These are mostly things I learn by pairing with
 smart people at [Hashrocket](http://hashrocket.com/).
 
-_486 TILs and counting..._
+_487 TILs and counting..._
 
 ---
 
@@ -240,6 +240,7 @@ _486 TILs and counting..._
 - [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)
+- [Generating UUIDs With pgcrypto](postgres/generating-uuids-with-pgcrypto.md)
 - [Get The Size Of A Database](postgres/get-the-size-of-a-database.md)
 - [Get The Size Of A Table](postgres/get-the-size-of-a-table.md)
 - [Get The Size Of An Index](postgres/get-the-size-of-an-index.md)

postgres/generating-uuids-with-pgcrypto.md

@@ -0,0 +1,33 @@
+# Generating UUIDs With pgcrypto
+
+If you check out the docs for the [`uuid-ossp`
+extension](https://www.postgresql.org/docs/current/static/uuid-ossp.html),
+you'll come across the following message.
+
+> The OSSP UUID library... is not well maintained, and is becoming
+> increasingly difficult to port to newer platforms. 
+
+A little bit later, it says:
+
+> If you only need randomly-generated (version 4) UUIDs, consider using the
+> gen_random_uuid() function from the pgcrypto module instead.
+
+So, if we are using the UUID data type and only need to generate random
+UUIDs, we can rely on the [`pgcrypto`
+extension](https://www.postgresql.org/docs/current/static/pgcrypto.html). It
+comes with the `gen_random_uuid()` function which generates random v4 UUIDs.
+
+```sql
+> create extension "pgcrypto";
+CREATE EXTENSION
+
+> select gen_random_uuid();
+           gen_random_uuid
+--------------------------------------
+ 0a557c31-0632-4d3e-a349-e0adefb66a69
+
+> select gen_random_uuid();
+           gen_random_uuid
+--------------------------------------
+ 83cdd678-8198-4d56-935d-d052f2e9db37
+```