Add Use Argument Indexes as a postgres til.

README.md

@@ -69,6 +69,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Timestamp Functions](postgres/timestamp-functions.md)
 - [Toggling The Pager In PSQL](postgres/toggling-the-pager-in-psql.md)
 - [Turning Timing On](postgres/turning-timing-on.md)
+- [Use Argument Indexes](postgres/use-argument-indexes.md)
 - [Using Intervals To Offset Time](postgres/using-intervals-to-offset-time.md)
 - [Who Is The Current User](postgres/who-is-the-current-user.md)
 - [Word Count for a Column](postgres/word-count-for-a-column.md)

postgres/use-argument-indexes.md

@@ -0,0 +1,24 @@
+# Use Argument Indexes
+
+In Postgres, each of the arguments you specify in a `select` statement has a
+1-based index tied to it. You can use these indexes in the `order by` and
+`group by` parts of the statement.
+
+Instead of writing
+
+```sql
+select id, updated_at from posts order by updated_at;
+```
+
+you can write
+
+```sql
+select id, updated_at from posts order by 2;
+```
+
+If you want to group by a table's `type` and then order by the counts from
+highest to lowest, you can do the following
+
+```sql
+select type, count(*) from transaction group by 1 order by 2 desc;
+```