Add Count Records By Type as a postgres til.

postgres/count-records-by-type.md

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+# Count Records By Type
+
+If you have a table with some sort of type column on it, you can come up
+with a count of the records in that table by type. You just need to take
+advantage of `group by`:
+
+```sql
+> select type, count(*) from pokemon group by type;
+
+  type   | count 
+-----------------
+ fire    |    10
+ water   |     4
+ plant   |     7
+ psychic |     3
+ rock    |    12
+```