Question

如何在Slick中表达COUNT（DISTINCT ...）？

我想构建此查询的等效内容：

sql"""select formatdatetime("timestamp",'yyyy.MM.dd'), count(distinct "order_id")
    from "sales" group by
    formatdatetime("timestamp",'yyyy.MM.dd')""".as[(String,Option[Int])]

我试过了：

val values = sales groupBy { entry =>
  formatDatetime(entry.timestamp, datetimeFormat)
} map { case(formattedDatetime, group) =>
  (formattedDatetime, group.distinctOn(_.orderId).length.?)
}

抛出运行时异常：

[info]   slick.SlickTreeException: Cannot convert node to SQL Comprehension
[info] | Path s9._2 : Vector[t2<{s3: Int', s4: java.sql.Timestamp', s5: scala.math.BigDecimal', s6: java.sql.Timestamp', s7: String', s8: String'}>]

（我用H2）

Answer 1

到目前为止，肯定有用/我最好的拍摄：

val countDistinctOrderId = SimpleExpression.nullary[Int] { queryBuilder =>
  import slick.util.MacroSupport._
  import queryBuilder._
  b"""count(distinct "order_id")"""
}
val values = sales groupBy { entry =>
  formatDatetime(entry.timestamp, datetimeFormat)
} map { case(formattedDatetime, group) =>
  (formattedDatetime, countDistinctOrderId.?)
}

Slick中的COUNT（DISTINCT ...）

1 个答案: