Add List All Columns Of A Specific Type as a postgres til.

README.md

@@ -60,6 +60,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Extracting Nested JSON Data](postgres/extracting-nested-json-data.md)
 - [Generate Series Of Numbers](postgres/generate-series-of-numbers.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)
 - [Temporarily Disable Triggers](postgres/temporarily-disable-triggers.md)
 - [Timestamp Functions](postgres/timestamp-functions.md)

postgres/list-all-columns-of-a-specific-type.md

@@ -0,0 +1,28 @@
+# List All Columns Of A Specific Type
+
+We can access information about all the columns in our database through the
+`information_schema` tables; in particular, the `columns` table. After
+connecting to a particular database, we can list all columns (across all our
+tables) of a specific type. We just need to know the schema of the tables we
+are interested in and the type that we want to track down.
+
+My application's tables are under the `public` schema and I want to track
+down all `timestamp` columns. My query can look something like this
+
+```sql
+> select table_name, column_name, data_type from information_schema.columns where table_schema = 'public' and data_type = 'timestamp without time zone';
+   table_name    | column_name |          data_type
+-----------------+-------------+-----------------------------
+ articles        | created_at  | timestamp without time zone
+ articles        | updated_at  | timestamp without time zone
+ users           | created_at  | timestamp without time zone
+ users           | updated_at  | timestamp without time zone
+(4 rows)
+```
+
+Alternatively, I could look for both `timestamp` and `timestamptz` with a
+query like this
+
+```sql
+> select table_name, column_name, data_type from information_schema.columns where table_schema = 'public' and data_type like '%timestamp%';
+```