Add Convert A String To A Timestamp as a postgres til

postgres/convert-a-string-to-a-timestamp.md

@@ -0,0 +1,31 @@
+# Convert A String To A Timestamp
+
+If you have a string that represents a point in time, there are a couple
+ways that you can convert it to a PostgreSQL `timestamptz` value.
+
+If the string is in [ISO 8601
+format](https://en.wikipedia.org/wiki/ISO_8601), then it can be simply cast
+to `timestamptz`.
+
+```sql
+> select '2018-10-24'::timestamptz;
+      timestamptz
+------------------------
+ 2018-10-24 00:00:00-05
+```
+
+A more general purpose approach is to use the
+[`to_timestamp`](https://www.postgresql.org/docs/11/static/functions-formatting.html)
+function.
+
+```sql
+> select to_timestamp('2018-10-24', 'YYYY-MM-DD');
+      to_timestamp
+------------------------
+ 2018-10-24 00:00:00-05
+```
+
+The first argument is our string-to-be-converted in whatever format. The
+second argument is another string describing in what format that string is.
+
+Note: Both of these approaches produce a `timestamptz` value.