4.2.7. Aggregate Expressions

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/18/sql-expressions.html
Description:

Can you add a code block with an example?

Perhaps something like this:

```psql
db=# WITH vals (f1) AS ( VALUES (1),(3),(4),(3),(2),(null) )
SELECT count(*), count(f1), COUNT(DISTINCT f1) FROM vals;

count | count | count
-------+-------+-------
6 | 5 | 4
(1 row)
```

After:

>> For example, count(*) returns the total number of input rows; count(f1)
returns the number of input rows in which f1 is not null, since count
ignores null values; and count(distinct f1) returns the number of distinct
non-null values of f1.

We haven’t seen the term “f1” before—and the paragraph doesn’t specify that
this is a field.