Add Extracting Nested JSON Data as a postgres til.

README.md

@@ -52,6 +52,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 
 ### postgres
 
+- [Extracting Nested JSON Data](postgres/extracting-nested-json-data.md)
 - [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)

postgres/extracting-nested-json-data.md

@@ -0,0 +1,26 @@
+# Extracting Nested JSON Data
+
+If you are storing nested JSON data in a postgres JSON column, you are
+likely going to find yourself in a situation where you need to access some
+of those nested values in your database code. For instance, you may need to
+get at the license number in this JSON column
+
+```sql
+  owner
+------------------------------------------------------------------------------
+{ "name": "Jason Borne", "license": { "number": "T1234F5G6", "state": "MA" } }
+```
+
+Unfortunately, the `->` operator isn't going to do the trick. You need the
+`json_extract_path` function
+
+```sql
+> select json_extract_path(owner, 'license', 'number') from some_table;
+
+ json_extract_path
+-------------------
+    T1234F5G6
+```
+
+Read more about [JSON Functions and
+Operators](http://www.postgresql.org/docs/9.4/static/functions-json.html).