Add Integers In Postgres as a postgres til.

postgres/integers-in-postgres.md

@@ -0,0 +1,32 @@
+# Integers In Postgres
+
+Postgres has three kinds of integers. Or rather three sizes of integers.
+There are `smallint` (`int2`), `integer` (`int4`), and `bigint` (`int8`)
+integers. As you might expect, they are 2 byte, 4 byte, and 8 byte integers
+respectively. They are also signed integers. All of this has implications
+for what ranges of integers can be represented by each type.
+
+The `smallint` integers have 2 bytes to use, so they can be used to
+represent integers from -32768 to +32767.
+
+The `integer` integers have 4 bytes to use, so they can be used to represent
+integers from -2147483648 to +2147483647.
+
+The `bigint` integers have 8 bytes to use, so they can be used to represent
+integers from -9223372036854775808 to +9223372036854775807.
+
+Though columns can be restricted to use a particular-sized integer, postgres
+is smart enough to default to `integer` and only use `bigint` as necessary
+when working with integers on the fly.
+
+```sql
+> select pg_typeof(55);
+ pg_typeof
+-----------
+ integer
+
+> select pg_typeof(99999999999999999);
+ pg_typeof
+-----------
+ bigint
+```