Add Defining Arrays as a postgres til.

README.md

@@ -77,6 +77,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Configure The Timezone](postgres/configure-the-timezone.md)
 - [Count Records By Type](postgres/count-records-by-type.md)
 - [Default Schema](postgres/default-schema.md)
+- [Defining Arrays](postgres/defining-arrays.md)
 - [Edit Existing Functions](postgres/edit-existing-functions.md)
 - [Extracting Nested JSON Data](postgres/extracting-nested-json-data.md)
 - [Fizzbuzz With Common Table Expressions](postgres/fizzbuzz-with-common-table-expressions.md)

postgres/defining-arrays.md

@@ -0,0 +1,33 @@
+# Defining Arrays
+
+In postgres, an array can be defined using the `array` syntax like so:
+
+```sql
+> select array['a','b','c'];
+  array
+---------
+ {a,b,c}
+```
+
+If you are inserting into an existing array column, you can use the array
+literal syntax.
+
+```sql
+> create temp table favorite_numbers(numbers integer[]);
+CREATE TABLE
+> insert into favorite_numbers values( '{7,3,9}' );
+INSERT 0 1
+> select numbers[2] from favorite_numbers;
+ numbers
+---------
+       3
+```
+
+Postgres also supports two-dimensional arrays.
+
+```sql
+select array[[1,2,3],[4,5,6],[7,8,9]] telephone;
+         telephone
+---------------------------
+ {{1,2,3},{4,5,6},{7,8,9}}
+```