Add Storing Emails With citext 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/).
 
-_376 TILs and counting..._
+_377 TILs and counting..._
 
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@@ -206,6 +206,7 @@ _376 TILs and counting..._
 - [Sets With The Values Command](postgres/sets-with-the-values-command.md)
 - [Sleeping](postgres/sleeping.md)
 - [Special Math Operators](postgres/special-math-operators.md)
+- [Storing Emails With citext](postgres/storing-emails-with-citext.md)
 - [String Contains Another String](postgres/string-contains-another-string.md)
 - [Temporarily Disable Triggers](postgres/temporarily-disable-triggers.md)
 - [Temporary Tables](postgres/temporary-tables.md)

postgres/storing-emails-with-citext.md

@@ -0,0 +1,35 @@
+# Storing Emails With citext
+
+Email addresses should be treated as case-insensitive because they are. If a
+user is trying to sign in with their email address, we shouldn't care if
+they type `[email protected]` or `[email protected]`. Both of those email
+addresses should be treated as equal and ultimately lead us to the same
+`User` record.
+
+With the
+[`citext`](http://www.postgresql.org/docs/current/static/citext.html)
+extension, we can create a column that acts as a case-insensitive text type.
+Any comparisons on a column of that type will internally have the `lower`
+function executed on the arguments.
+
+The following example shows this in action:
+
+```sql
+create extension if not exists citext;
+
+create table citext_emails (
+  id serial primary key,
+  email citext not null unique
+);
+
+insert into citext_emails (email) values ('[email protected]');
+
+select * from citext_emails where email = '[email protected]';
+--  id |      email
+-- ----+------------------
+--   1 | [email protected]
+```
+
+See
+[`citext-emails.sql`](https://github.com/jbranchaud/postgresing/blob/master/citext-emails.sql)
+for a full example.