Add Checking The Type Of A Value as a postgres til.

postgres/checking-the-type-of-a-value.md

@@ -0,0 +1,41 @@
+# Checking The Type Of A Value
+
+The `pg_typeof()` function allows you to determine the data type of anything
+in Postgres.
+
+```sql
+> select pg_typeof(1);
+ pg_typeof
+-----------
+ integer
+(1 row)
+
+> select pg_typeof(true);
+ pg_typeof
+-----------
+ boolean
+(1 row)
+```
+
+If you try it on an arbitrary string, it is unable to disambiguate which
+string type (e.g. `text` vs `varchar`).
+
+```sql
+> select pg_typeof('hello');
+ pg_typeof
+-----------
+ unknown
+(1 row)
+```
+
+You just have to be a bit more specific.
+
+```sql
+> select pg_typeof('hello'::varchar);
+     pg_typeof
+-------------------
+ character varying
+(1 row)
+```
+
+[source](http://www.postgresql.org/docs/9.3/static/functions-info.html#FUNCTIONS-INFO-CATALOG-TABLE)