Major Description
Quoted column names like `a``b.c` cannot be represented with col(), $"<name>" and df("") because they don't handle such column names properly.
For example, if we have a following DataFrame.
val df1 = spark.sql("SELECT 'col1' AS `a``b.c`")
For the DataFrame, this query is successfully executed.
scala> df1.selectExpr("`a``b.c`").show
+-----+
|a`b.c|
+-----+
| col1|
+-----+
But the following query will fail because df1("`a``b.c`") throws an exception.
scala> df1.select(df1("`a``b.c`")).show
org.apache.spark.sql.AnalysisException: syntax error in attribute name: `a``b.c`;
at org.apache.spark.sql.catalyst.analysis.UnresolvedAttribute$.e$1(unresolved.scala:152)
at org.apache.spark.sql.catalyst.analysis.UnresolvedAttribute$.parseAttributeName(unresolved.scala:162)
at org.apache.spark.sql.catalyst.plans.logical.LogicalPlan.resolveQuoted(LogicalPlan.scala:121)
at org.apache.spark.sql.Dataset.resolve(Dataset.scala:221)
at org.apache.spark.sql.Dataset.col(Dataset.scala:1274)
at org.apache.spark.sql.Dataset.apply(Dataset.scala:1241)
... 49 elided
