object ProductTable extends Table[(Int,String,Double,java.sql.Date,Int,Option[Int],Boolean)]("products") {
  def id = column[Int]("productId",O.PrimaryKey,O.AutoInc)
  def title = column[String]("title")
  def description = column[String]("description")
  def shortDescription = column[String]("shortDescription")
  def price = column[Double]("price")
  def addedDate = column[java.sql.Date]("addedDate")
  def brandId = column[Int]("brandId")
  def defaultImageId = column[Option[Int]]("defaultImageId")
  def visitCounter = column[Int]("visitCounter")
  def archived = column[Boolean]("archived")
  def * = id ~ title ~ description ~ shortDescription ~ price ~ addedDate ~ brandId ~ defaultImageId ~ visitCounter ~ archived
}

我需要一个简单的查询,从数据库中选择8行：

ProductTable.filter(_.title === "something")
  .sortBy(_.visitCounter)
  .map(_.title)
  .take(8)
  .selectStatement

输出是：

select x2.x3 from 
   (select x4.`title` as x3 from `products` x4 
     where x4.`title` = 'something' 
     order by x4.`visitCounter` limit 8) x2

如果我摆脱了take()方法：

ProductTable.filter(_.title === "something")
 .sortBy(_.visitCounter)
 .map(_.title)
 .selectStatement

然后输出是：

select x2.`title` from `products` x2 
where x2.`title` = 'something' 
order by x2.`visitCounter`

所以我的问题是：为什么Slick在使用take()方法构造查询对象时会生成子查询？

附：如果它可以相关,我使用MysqL驱动程序与所有这些