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32 lines
1.0 KiB
Markdown
32 lines
1.0 KiB
Markdown
# Group By The Result Of A Function Call
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Typically, a query that I write involving a `group by` will look more or less
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like this:
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```sql
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select category, count(*)
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from products
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group by category;
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```
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The `category` column is the thing I'm grouping by. In this case, I'm doing a
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little data exploration.
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We are not strictly limited to grouping by a column. We can use all sorts of
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functions offered by Postgres to get at more interesting results. [String
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functions](https://www.postgresql.org/docs/current/functions-string.html) are a
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great place to start.
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Let's say our `products` table also has an `identifier` column with a naming
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scheme where the first three letters of the identifier correspond to the
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product's classification. We can group by that part of the `identifier`:
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```sql
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select substring(identifier from 1 for 3), count(*)
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from products
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group by substring(identifier from 1 for 3);
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```
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The funkiness of the `substring` syntax aside, we were able to group our
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products in a new way and learn something about our data.
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