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[SPARK-6459][SQL] Warn when constructing trivially true equals predicate #5163

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[SPARK-6459][SQL] Warn when constructing trivially true equals predicate #5163

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1b57e8d
Warn when constructing trivially true equals predicate
marmbrus Mar 24, 2015
16c1f0b
fix visibility
marmbrus Mar 24, 2015
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13 changes: 11 additions & 2 deletions sql/core/src/main/scala/org/apache/spark/sql/Column.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -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}
Expand All @@ -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)
Expand Down Expand Up @@ -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.
Expand Down