cloud-fan commented on a change in pull request #29795:
URL: https://github.com/apache/spark/pull/29795#discussion_r492189437
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File path: sql/core/src/main/scala/org/apache/spark/sql/Column.scala
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@@ -901,39 +901,125 @@ class Column(val expr: Expression) extends Logging {
* // result: org.apache.spark.sql.AnalysisException: Ambiguous reference
to fields
* }}}
*
+ * This method supports adding/replacing nested fields directly e.g.
+ *
+ * {{{
+ * val df = sql("SELECT named_struct('a', named_struct('a', 1, 'b', 2))
struct_col")
+ * df.select($"struct_col".withField("a.c", lit(3)).withField("a.d",
lit(4)))
+ * // result: {"a":{"a":1,"b":2,"c":3,"d":4}}
+ * }}}
+ *
+ * However, if you are going to add/replace multiple nested fields, it is
more optimal to extract
+ * out the nested struct before adding/replacing multiple fields e.g.
+ *
+ * {{{
+ * val df = sql("SELECT named_struct('a', named_struct('a', 1, 'b', 2))
struct_col")
+ * df.select($"struct_col".withField("a", $"struct_col.a".withField("c",
lit(3)).withField("d", lit(4))))
+ * // result: {"a":{"a":1,"b":2,"c":3,"d":4}}
+ * }}}
+ *
Review comment:
I think the same issue happens in `withColumn` as well. I'm fine with
method doc.
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