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# Group By The Result Of A Function Call

Typically, a query that I write involving a `group by` will look more or less like this:

```sql
select category, count(*)
  from products
  group by category;
```

The `category` column is the thing I'm grouping by. In this case, I'm doing a little data exploration.

We are not strictly limited to grouping by a column. We can use all sorts of functions offered by Postgres to get at more interesting results. [String functions](https://www.postgresql.org/docs/current/functions-string.html) are a great place to start.

Let's say our `products` table also has an `identifier` column with a naming scheme where the first three letters of the identifier correspond to the product's classification. We can group by that part of the `identifier`:

```sql
select substring(identifier from 1 for 3), count(*)
  from products
  group by substring(identifier from 1 for 3);
```

The funkiness of the `substring` syntax aside, we were able to group our products in a new way and learn something about our data.


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