Add Count How Many Records There Are Of Each Type as a postgres til

postgres/count-how-many-records-there-are-of-each-type.md

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+# Count How Many Records There Are Of Each Type
+
+Let's say I have a `books` table full of data. One of the columns on this table
+is `status` which represents whether the book is published, in review, or still
+a draft.
+
+We can find out how many records (books) there are for each `status` using a
+`group by` clause and the `count` aggregate function.
+
+```sql
+> select status, count(*)
+    from books
+    group by status;
+
+  status   | count
+-----------+-------
+ ø         |   123
+ published |   611
+ draft     |   364
+ review    |   239
+(4 rows)
+```
+
+Because we don't have a `not null` constraint on the `status` column, there are
+also some records that have a null value.
+
+We can take this a step further by ordering the output in a consistent
+way—descending order of the count column.
+
+```sql
+> select status, count(*)
+    from books
+    group by status
+    order by 2 desc;
+
+  status   | count
+-----------+-------
+ published |   611
+ draft     |   364
+ review    |   239
+ ø         |   123
+(4 rows)
+```
+
+This `order by` clauses uses [a positional index from the select
+arguments](use-argument-indexes.md), so the `2` references the `count(*)`
+argument.