我不认为这需要什么 leg 以及 lead 功能。你可以通过 join 我也是。检查以下代码以供参考：
注意：我在中添加了更多数据 kafkaDF 更多了解。

scala> kafkaDf.show(false)
+---------+----+-------+-----+----------+
|companyId|year|quarter|sales|prev_sales|
+---------+----+-------+-----+----------+
|15       |2016|4      |100.5|          |
|15       |2016|1      |115.8|          |
|15       |2016|3      |150.1|          |
+---------+----+-------+-----+----------+

scala> cassandraTabledf.show
+---------+----+-------+-----+----------+
|companyId|year|quarter|sales|prev_sales|
+---------+----+-------+-----+----------+
|       15|2016|      3|120.6|     320.6|
|       15|2016|      2|450.2|     650.2|
|       15|2016|      1|200.7|     700.7|
|       15|2015|      4|221.4|       400|
|       15|2015|      3|320.6|       300|
|       15|2015|      2|650.2|       200|
|       15|2015|      1|700.7|       100|
+---------+----+-------+-----+----------+

scala>kafkaDf.alias("k").join(
                              cassandraTabledf.alias("c"), 
                              col("k.companyId") === col("c.companyId") && 
                              col("k.quarter") === col("c.quarter") && 
                              (col("k.year") - 1) === col("c.year"),
                              "left"
                             )
                       .drop("prev_sales")
                       .select(col("k.*"), col("c.sales").alias("prev_sales"))
                       .withColumn("prev_sales", when(col("prev_sales").isNull, col("sales")).otherwise(col("prev_sales")))
                       .show()
+---------+----+-------+-----+----------+
|companyId|year|quarter|sales|prev_sales|
+---------+----+-------+-----+----------+
|       15|2016|      1|115.8|     700.7|
|       15|2016|      3|150.1|     320.6|
|       15|2016|      4|100.5|     221.4|
+---------+----+-------+-----+----------+