Add Constructing A Range Of Dates as a postgres til

postgres/constructing-a-range-of-dates.md

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+# Constructing A Range Of Dates
+
+PostgreSQL offers a number of range types including the `daterange` type.
+This can be constructed using the `daterange()` function with two strings
+representing the lower and upper bounds of the date range respectively.
+
+```sql
+> select daterange('2015-1-1','2015-1-5');
+        daterange
+-------------------------
+ [2015-01-01,2015-01-05)
+```
+
+The lower bound is inclusive -- indicated by the `[` character -- and the
+upper bound is exclusive -- indicated by the `)` character.
+
+[source](http://www.postgresql.org/docs/current/static/rangetypes.html)