Add Compute Hashes With pgcrypto as a postgres til

Author: jbranchaud

README.md

@@ -130,6 +130,7 @@ _305 TILs and counting..._
 - [Aggregate A Column Into An Array](postgres/aggregate-a-column-into-an-array.md)
 - [Auto Expanded Display](postgres/auto-expanded-display.md)
 - [Checking The Type Of A Value](postgres/checking-the-type-of-a-value.md)
+- [Compute Hashes With pgcrypto](postgres/compute-hashes-with-pgcrypto.md)
 - [Configure The Timezone](postgres/configure-the-timezone.md)
 - [Count Records By Type](postgres/count-records-by-type.md)
 - [Create A Composite Primary Key](postgres/create-a-composite-primary-key.md)

postgres/compute-hashes-with-pgcrypto.md

@@ -0,0 +1,26 @@
+# Compute Hashes With pgcrypto
+
+The `pgcrypto` extension that comes with PostgreSQL adds access to some
+general hashing functions. Included are `md5`, `sha1`, `sha224`, `sha256`,
+`sha384` and `sha512`. Any of these hashing functions can be applied to an
+arbitrary string using the `digest` function. Here are example of the `md5`
+and `sha1` algorithms:
+
+```sql
+> create extension pgcrypto;
+CREATE EXTENSION
+
+> select digest('Hello, World!', 'md5');
+               digest
+------------------------------------
+ \x65a8e27d8879283831b664bd8b7f0ad4
+
+> select digest('Hello, World!', 'sha1');
+                   digest
+--------------------------------------------
+ \x0a0a9f2a6772942557ab5355d76af442f8f65e01
+```
+
+See the [`pgcrypto` docs](
+http://www.postgresql.org/docs/current/static/pgcrypto.html) for more
+details.