Add Using Intervals To Offset Time as a postgres til.

README.md

@@ -57,6 +57,7 @@ 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)
+- [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/using-intervals-to-offset-time.md

@@ -0,0 +1,21 @@
+# Using Intervals To Offset Time
+
+Postgres Intervals can be used with time as a way of determining a
+standard offset. For instance, I can concisely determine what the time was 2
+hours earlier with
+
+```sql
+> select now() - '2 hours'::interval as earlier;
+            earlier
+-------------------------------
+ 2015-06-12 21:17:43.678822-05
+```
+
+or similarly
+
+```sql
+> select now() - interval '2 hours' as earlier;
+            earlier
+-------------------------------
+ 2015-06-12 21:17:43.678822-05
+```