Add Intervals Of Time By Week as a postgres til.

README.md

@@ -61,6 +61,7 @@ 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)
+- [Intervals Of Time By Week](postgres/intervals-of-time-by-week.md)
 - [Limit Execution Time Of Statements](postgres/limit-execution-time-of-statements.md)
 - [List All Columns Of A Specific Type](postgres/list-all-columns-of-a-specific-type.md)
 - [String Contains Another String](postgres/string-contains-another-string.md)

postgres/intervals-of-time-by-week.md

@@ -0,0 +1,18 @@
+# Intervals Of Time By Week
+
+It is pretty common to use hours or days when creating a Postgres
+interval. However, intervals can also be created in week-sized chunks
+
+```sql
+> select '2 weeks'::interval;
+ interval
+----------
+ 14 days
+(1 row)
+
+> select make_interval(0,0,7,0,0,0,0);
+ make_interval
+---------------
+ 49 days
+(1 row)
+```