如何使用光滑进行聚合

Question

我想强制光滑创建像

select max(price) from coffees where ... 

但光滑的文档没有帮助

val q = Coffees.map(_.price) //this is query Query[Coffees.type, ...]
val q1 = q.min // this is Column[Option[Double]]
val q2 = q.max
val q3 = q.sum
val q4 = q.avg 

因为那些q1-q4不是查询,我无法获得结果,但可以在其他查​​询中使用它们.

这个说法

for {
  coffee <- Coffees
} yield coffee.price.max

生成正确的查询但不推荐使用(生成警告:"不推荐使用类ColumnExtensionMethods中的方法max:使用Query.max"). 如何在没有警告的情况下生成此类查询？

另一个问题是通过以下方式聚合:

"select name, max(price) from coffees group by name"

试图解决它

for {
  coffee <- Coffees
} yield (coffee.name, coffee.price.max)).groupBy(x => x._1)

产生

select x2.x3, x2.x3, x2.x4 from (select x5."COF_NAME" as x3, max(x5."PRICE") as x4 from "coffees" x5) x2 group by x2.x3

这会导致明显的db错误

column "x5.COF_NAME" must appear in the GROUP BY clause or be used in an aggregate function

如何生成这样的查询？

Answer 1

据我所知,第一个就是简单

Query(Coffees.map(_.price).max).first

第二个

val maxQuery = Coffees
  .groupBy { _.name }
  .map { case (name, c) =>
    name -> c.map(_.price).max
  }

maxQuery.list

要么

val maxQuery = for {
  (name, c) <- Coffees groupBy (_.name)
} yield name -> c.map(_.price).max

maxQuery.list