Add Getting A Slice Of An Array as a postgres til.

README.md

@@ -82,6 +82,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Extracting Nested JSON Data](postgres/extracting-nested-json-data.md)
 - [Fizzbuzz With Common Table Expressions](postgres/fizzbuzz-with-common-table-expressions.md)
 - [Generate Series Of Numbers](postgres/generate-series-of-numbers.md)
+- [Getting A Slice Of An Array](postgres/getting-a-slice-of-an-array.md)
 - [Integers In Postgres](postgres/integers-in-postgres.md)
 - [Intervals Of Time By Week](postgres/intervals-of-time-by-week.md)
 - [Limit Execution Time Of Statements](postgres/limit-execution-time-of-statements.md)

postgres/getting-a-slice-of-an-array.md

@@ -0,0 +1,25 @@
+# Getting A Slice Of An Array
+
+Postgres has a very natural syntax for grabbing a slice of an array. You
+simply add brackets after the array declaring the lower and upper bounds
+of the slice separated by a colon.
+
+```sql
+> select (array[4,5,6,7,8,9])[2:4];
+  array
+---------
+ {5,6,7}
+```
+
+Notice that the bounds are inclusive, the array index is `1`-based, and the
+array declaration above needs to be wrapped in parentheses in order to not
+trip up the array slice syntax.
+
+You can also select rectangular slices from two dimensional arrays like so:
+
+```sql
+> select (array[[1,2,3],[4,5,6],[7,8,9]])[2:3][1:2];
+     array
+---------------
+ {{4,5},{7,8}}
+```