Question

我在SQL中有以下2个SQL查询示例：

a) update DBTABLE1
    set col1 = 'Yes'
where ID IN ( '100' ) and City = any(select City from DBTable2 where Country = 'USA');

b) update DBTABLE1
    set col2 = 'No'
where ID NOT IN ( '100' ) and City = any(select City from DBTable2 where Country = 'USA');


How to write above 2 SQLs using Apache Spark Dataframes (Not Select subquery etc). A dataframe is already having these 2 columns - col1 and col2, I am changing their values using WITHCOLUMN and WHEN clause.

CitiDF包含城市数量的数据集。

I tried below but giving compile errors:

c) This is for (a) above:

withcolumn(col("col1"),when(col("id") === lit("100") 
and col("city").isin(CitiDF("city")), lit("yes")))

d) This is for (b) above:

withcolumn(col("col2"),when(col("id") === lit("100") 
and ! (col("city").isin(CitiDF("city"))), lit("yes")))

Answer 1

为使事情更具体，让我们考虑一些玩具数据。我们有一个名为df的DataFrame，它看起来像这样：

+---+---------+------+------+
| id|     city|  col1|  col2|
+---+---------+------+------+
|100|Frankfurt|filler|filler|
|200|   Berlin|filler|filler|
|100|   Vienna|filler|filler|
|500| Victoria|filler|filler|
|600| Shanghai|filler|filler|
|100|  Cologne|filler|filler| 
+---+---------+------+------+

另一个名为cities，看起来像这样：

+---------+
| cityName|
+---------+
|Frankfurt|
|   Vienna|
+---------+

我们可以像这样进行您的查询：

val cityList = cities.collect.map(x => x(0))
val df1 = df.withColumn("col1", when($"id" === "100" and $"city".isin(cityList: _*), "yes"))

我们得到的结果是：

+---+---------+----+------+
| id|     city|col1|  col2|
+---+---------+----+------+
|100|Frankfurt| yes|filler|
|200|   Berlin|null|filler|
|100|   Vienna| yes|filler|
|500| Victoria|null|filler|
|600| Shanghai|null|filler|
|100|  Cologne|null|filler|
+---+---------+----+------+

对于第二个查询，我们使用相同的cityList：

val df2 = df.withColumn("col2", when($"id" === "100" and !$"city".isin(cityList: _*), "yes"))

给予我们

+---+---------+------+----+
| id|     city|  col1|col2|
+---+---------+------+----+
|100|Frankfurt|filler|null|
|200|   Berlin|filler|null|
|100|   Vienna|filler|null|
|500| Victoria|filler|null|
|600| Shanghai|filler|null|
|100|  Cologne|filler| yes|
+---+---------+------+----+

但是，这种方法有一个很大的警告。如果城市数量很多，那么收集所有名称可能会耗尽内存。相反，我会考虑使用其他方法，例如外部联接：

df.join(cities, df("city") === cities("cityName"), "outer").
  withColumn("col1", when($"cityName".isNotNull and $"id" === "100", "yes")).
  withColumn("col2", when($"cityName".isNull and $"id" === "100", "yes")).
  drop("cityName")

给予我们

+---+---------+----+----+
| id|     city|col1|col2|
+---+---------+----+----+
|100|Frankfurt| yes|null|
|500| Victoria|null|null|
|200|   Berlin|null|null|
|100|   Vienna| yes|null|
|100|  Cologne|null| yes|
|600| Shanghai|null|null|
+---+---------+----+----+

是的，它引入了一个额外的列，但只是暂时的，并且避免了将潜在的大量城市列表拖入驾驶员的记忆中。

Answer 2

使用Jason所使用的示例数据并且无需在外部混合列表，则可以使用spark-sql本身来实现解决方案。检查一下：

val df = Seq((100,"Frankfurt","filler","filler"),(200,"Berlin","filler","filler"),(100,"Vienna","filler","filler"),(500,"Victoria","filler","filler"),(600,"Shanghai","filler","filler"),(100,"Cologne","filler","filler")).toDF("id","city","col1","col2")
df.createOrReplaceTempView("city_details")
val city = Seq(("Frankfurt"),("Vienna")).toDF("cityName")
city.createOrReplaceTempView("city_list")
df.show(false)
spark.sql(
  """ select id,city, case when id=100 and array_contains((select collect_list(cityname) from city_list), city) then 'yes' else null end as col1,
      case when id=100 and not array_contains((select collect_list(cityname) from city_list), city) then 'yes' else null end as col2
      from city_details
  """).show(false)

输出：

+---+---------+----+----+
|id |city     |col1|col2|
+---+---------+----+----+
|100|Frankfurt|yes |null|
|200|Berlin   |null|null|
|100|Vienna   |yes |null|
|500|Victoria |null|null|
|600|Shanghai |null|null|
|100|Cologne  |null|yes |
+---+---------+----+----+

如何使用Apache Spark数据帧写入和不写入

2 个答案: