我有2個表:主要和更新與列名稱,ID和部門。 我想先閱讀主表,如果部門字段值爲空,我可以從更新表讀取它。斯卡拉光滑 - 如何從不同的表中獲取列值
例如,從下表中,我應該從Update表中獲取KING的部門值。
如何實現這個使用scala slick與運行普通sql查詢?
主要
+-------+----+------------+
+ name | id | department +
+-------+----+------------+
| KING | 10 | |
| BLAKE | 30 | SALES |
+-------+----+------------+
更新
+-------+----+------------+
+ name | id | department +
+-------+----+------------+
| KING | 10 | SYSTEMS |
| BLAKE | 30 | SALES |
+-------+----+------------+
這裏是普通的SQL查詢
SELECT
m.`name`,
m.`id`,
if(m.`department`='', u.`department`) as `department`
FROM `Main` m
FROM `Update` u ON m.id=u.id
我有如下到目前爲止定義的代碼...
case class Main(name: Option[String],
id: Option[int],
department: Option[String])
case class Update(name: Option[String],
id: Option[int],
department: Option[String])
lazy val mainQuery = TableQuery[MainTableDefinition]
lazy val updateQuery = TableQuery[UpdateTableDefinition]
class MainTableDefinition(tag: Tag) extends Table[Main](tag, "Main") {
def name = column[Option[String]]("name")
def id = column[Option[int]]("id")
def department = column[Option[String]]("department")
override def * =
(name, id, department)<> (Main.tupled, Main.unapply)
}
class UpdateTableDefinition(tag: Tag) extends Table[Update](tag, "Update") {
def name = column[Option[String]]("name")
def id = column[Option[int]]("id")
def department = column[Option[String]]("department")
override def * =
(name, id, department)<> (Update.tupled, Update.unapply)
}
val query = for {
m <- mainQuery
u <- updateQuery if m.id === u.id
} yield (m, u)
db.run(query.to[List].result)
您可能想要定義自定義函數'coalesce'(https://www.postgresql.org/docs/9.2/static/functions-conditional.html)並使用它'''val query = for { m < - mainQuery u < - updateQuery如果m.id === u.id department = coalesce(m.department,u.department) } yield(m.id,department)''' –