问题是不清楚的数据方面，这里是一个方法的基础上作出的一些假设。不，不是用case，而是用另一种方式。

编码

import spark.implicits._
import org.apache.spark.sql.functions._

// Unclear if code is asc or unique, otherwise a zipWithIndex needed. 
// Assumed code c can be used, seems that we just need to look for RW and it is after the ST.

val df = spark.sparkContext.parallelize(Seq( (1,7,"ST"), (1,8,"XX"), (1,9,"RW"), (3,10,"ST"), (3,11,"AA"), (3,12,"RW"), (2,3,"ST"), (2,4,"TT"))).toDF("i", "c", "t")
df.createOrReplaceTempView("data")

val res = spark.sql(""" SELECT i as iN
                          FROM data
                         WHERE t = 'RW' 
                    """)
val temp = df.join(res, df("i") === res("iN"), "outer")
val results = temp.withColumn("openST", when(col("iN").isNull && col("t") === lit("ST"), lit("ST")).otherwise("")).select($"i", $"c", $"t", $"openST")
results.show(false)

结果

+---+---+---+------+
|i  |c  |t  |openST|
+---+---+---+------+
|1  |7  |ST |      |
|1  |8  |XX |      |
|1  |9  |RW |      |
|2  |3  |ST |ST    |
|2  |4  |TT |      |
|3  |10 |ST |      |
|3  |11 |AA |      |
|3  |12 |RW |      |
+---+---+---+------+