diff --git a/sql/core/src/main/scala/org/apache/spark/sql/Column.scala b/sql/core/src/main/scala/org/apache/spark/sql/Column.scala index 2ae47e07d45ec83c0cfd4bf17aa8c43f4ca0f3fe..3cd7adf8cab5ecb4d8fb1c974c2a787680878607 100644 --- a/sql/core/src/main/scala/org/apache/spark/sql/Column.scala +++ b/sql/core/src/main/scala/org/apache/spark/sql/Column.scala @@ -20,6 +20,7 @@ package org.apache.spark.sql import scala.language.implicitConversions import org.apache.spark.annotation.Experimental +import org.apache.spark.Logging import org.apache.spark.sql.functions.lit import org.apache.spark.sql.catalyst.expressions._ import org.apache.spark.sql.catalyst.analysis.{UnresolvedAttribute, UnresolvedStar, UnresolvedGetField} @@ -46,7 +47,7 @@ private[sql] object Column { * @groupname Ungrouped Support functions for DataFrames. */ @Experimental -class Column(protected[sql] val expr: Expression) { +class Column(protected[sql] val expr: Expression) extends Logging { def this(name: String) = this(name match { case "*" => UnresolvedStar(None) @@ -109,7 +110,15 @@ class Column(protected[sql] val expr: Expression) { * * @group expr_ops */ - def === (other: Any): Column = EqualTo(expr, lit(other).expr) + def === (other: Any): Column = { + val right = lit(other).expr + if (this.expr == right) { + logWarning( + s"Constructing trivially true equals predicate, '${this.expr} = $right'. " + + "Perhaps you need to use aliases.") + } + EqualTo(expr, right) + } /** * Equality test.