Add Aggregate A Column Into An Array as a postgres til.

README.md

@@ -115,6 +115,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 
 - [A Better Null Display Character](postgres/a-better-null-display-character.md)
 - [Adding Composite Uniqueness Constraints](postgres/adding-composite-uniqueness-constraints.md)
+- [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)
 - [Configure The Timezone](postgres/configure-the-timezone.md)

postgres/aggregate-a-column-into-an-array.md

@@ -0,0 +1,29 @@
+# Aggregate A Column Into An Array
+
+PostgreSQL's `array_agg` function can be used to aggregate a column into an
+array. Consider the following column:
+
+```sql
+> select num from generate_series(1,5) as num;
+ num
+-----
+   1
+   2
+   3
+   4
+   5
+```
+
+By wrapping the `array_agg` aggregate function around `num` we are able to
+*aggregate* the values in that column into an array, like so:
+
+```sql
+> select array_agg(num) from generate_series(1,5) as num;
+  array_agg
+-------------
+ {1,2,3,4,5}
+```
+
+See the docs on [aggregate
+functions](http://www.postgresql.org/docs/current/static/functions-aggregate.html)
+for more details.