# 14.6\. 聚集函數 HQL查詢甚至可以返回作用于屬性之上的聚集函數的計算結果: ``` select avg(cat.weight), sum(cat.weight), max(cat.weight), count(cat) from Cat cat ``` 受支持的聚集函數如下： * `avg(...), sum(...), min(...), max(...)` * `count(*)` * `count(...), count(distinct ...), count(all...)` 你可以在選擇子句中使用數學操作符、連接以及經過驗證的SQL函數： ``` select cat.weight + sum(kitten.weight) from Cat cat join cat.kittens kitten group by cat.id, cat.weight ``` ``` select firstName||' '||initial||' '||upper(lastName) from Person ``` 關鍵字`distinct`與`all` 也可以使用，它們具有與SQL相同的語義. ``` select distinct cat.name from Cat cat select count(distinct cat.name), count(cat) from Cat cat ```