## 2.7. Aggregate Functions

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 Like most other relational database products, PostgreSQL supports *aggregate functions*. An aggregate function computes a single result from multiple input rows. For example, there are aggregates to compute the `count`, `sum`, `avg` (average), `max` (maximum) and `min` (minimum) over a set of rows.

 As an example, we can find the highest low-temperature reading anywhere with:

```
SELECT max(temp_lo) FROM weather;

```

```
 max
