Add Counting Records With Ecto as an elixir 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/).
 
-_500 TILs and counting..._
+_501 TILs and counting..._
 
 ---
 
@@ -87,6 +87,7 @@ _500 TILs and counting..._
 - [Assert An Exception Is Raised](elixir/assert-an-exception-is-raised.md)
 - [Binary Representation Of A String](elixir/binary-representation-of-a-string.md)
 - [Check For A Substring Match](elixir/check-for-a-substring-match.md)
+- [Counting Records With Ecto](elixir/counting-records-with-ecto.md)
 - [Create A Date With The Date Sigil](elixir/create-a-date-with-the-date-sigil.md)
 - [Creating Indexes With Ecto](elixir/creating-indexes-with-ecto.md)
 - [Determine The Latest Release Of A Hex Package](elixir/determine-the-latest-release-of-a-hex-package.md)

elixir/counting-records-with-ecto.md

@@ -0,0 +1,40 @@
+# Counting Records With Ecto
+
+Sometimes you want to know how many records there are in a table. Ecto gives
+us a couple ways to approach this.
+
+We can use the
+[`count\1`](https://hexdocs.pm/ecto/Ecto.Query.API.html#count/1) function
+that the Ecto query API provides.
+
+```elixir
+> Repo.one(from p in "people", select: count(p.id))
+
+16:09:52.759 [debug] QUERY OK source="people" db=1.6ms
+SELECT count(p0."id") FROM "people" AS p0 []
+168
+```
+
+Alternatively, we can use the
+[`fragment/1`](https://hexdocs.pm/ecto/Ecto.Query.API.html#fragment/1)
+function to use PostgreSQL's `count` function.
+
+```elixir
+> Repo.one(from p in "people", select: fragment("count(*)"))
+
+16:11:19.818 [debug] QUERY OK source="people" db=1.5ms
+SELECT count(*) FROM "people" AS p0 []
+168
+```
+
+Lastly, `Ecto.Repo` has the
+[`aggregate/4`](https://hexdocs.pm/ecto/Ecto.Repo.html#c:aggregate/4)
+function which provides a `:count` option.
+
+```elixir
+> Repo.aggregate(from(p in "people"), :count, :id)
+
+16:11:23.786 [debug] QUERY OK source="people" db=1.7ms
+SELECT count(p0."id") FROM "people" AS p0 []
+168
+```