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From GitBox <...@apache.org>
Subject [GitHub] [spark] viirya commented on a change in pull request #33040: [SPARK-35290][SQL] Append new nested struct fields rather than sort for unionByName with null filling
Date Wed, 23 Jun 2021 17:15:41 GMT

viirya commented on a change in pull request #33040:
URL: https://github.com/apache/spark/pull/33040#discussion_r657307794



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/ResolveUnion.scala
##########
@@ -20,137 +20,66 @@ package org.apache.spark.sql.catalyst.analysis
 import scala.collection.mutable
 
 import org.apache.spark.sql.catalyst.expressions._
-import org.apache.spark.sql.catalyst.optimizer.{CombineUnions, OptimizeUpdateFields}
+import org.apache.spark.sql.catalyst.optimizer.{CombineUnions}
 import org.apache.spark.sql.catalyst.plans.logical.{LogicalPlan, Project, Union}
 import org.apache.spark.sql.catalyst.rules.Rule
 import org.apache.spark.sql.catalyst.trees.TreePattern.UNION
 import org.apache.spark.sql.errors.QueryCompilationErrors
 import org.apache.spark.sql.types._
 import org.apache.spark.sql.util.SchemaUtils
-import org.apache.spark.unsafe.types.UTF8String
 
 /**
  * Resolves different children of Union to a common set of columns.
  */
 object ResolveUnion extends Rule[LogicalPlan] {
   /**
-   * This method sorts columns recursively in a struct expression based on column names.
+   * Adds missing fields recursively into given `col` expression, based on the expected struct
+   * fields from merging the two schemas. This is called by `compareAndAddFields` when we
find two
+   * struct columns with same name but different nested fields. This method will recursively
+   * return a new struct with all of the expected fields, adding null values when `col` doesn't
+   * already contain them. Currently we don't support merging structs nested inside of arrays
+   * or maps.
    */
-  private def sortStructFields(expr: Expression): Expression = {
-    val existingExprs = expr.dataType.asInstanceOf[StructType].fieldNames.zipWithIndex.map
{
-      case (name, i) =>
-        val fieldExpr = GetStructField(KnownNotNull(expr), i)
-        if (fieldExpr.dataType.isInstanceOf[StructType]) {
-          (name, sortStructFields(fieldExpr))
-        } else {
-          (name, fieldExpr)
-        }
-    }.sortBy(_._1).flatMap(pair => Seq(Literal(pair._1), pair._2))
-
-    val newExpr = CreateNamedStruct(existingExprs)
-    if (expr.nullable) {
-      If(IsNull(expr), Literal(null, newExpr.dataType), newExpr)
-    } else {
-      newExpr
-    }
-  }
-
-  /**
-   * Assumes input expressions are field expression of `CreateNamedStruct`. This method
-   * sorts the expressions based on field names.
-   */
-  private def sortFieldExprs(fieldExprs: Seq[Expression]): Seq[Expression] = {
-    fieldExprs.grouped(2).map { e =>
-      Seq(e.head, e.last)
-    }.toSeq.sortBy { pair =>
-      assert(pair.head.isInstanceOf[Literal])
-      pair.head.eval().asInstanceOf[UTF8String].toString
-    }.flatten
-  }
-
-  /**
-   * This helper method sorts fields in a `UpdateFields` expression by field name.
-   */
-  private def sortStructFieldsInWithFields(expr: Expression): Expression = expr transformUp
{
-    case u: UpdateFields if u.resolved =>
-      u.evalExpr match {
-        case i @ If(IsNull(_), _, CreateNamedStruct(fieldExprs)) =>
-          val sorted = sortFieldExprs(fieldExprs)
-          val newStruct = CreateNamedStruct(sorted)
-          i.copy(trueValue = Literal(null, newStruct.dataType), falseValue = newStruct)
-        case CreateNamedStruct(fieldExprs) =>
-          val sorted = sortFieldExprs(fieldExprs)
-          val newStruct = CreateNamedStruct(sorted)
-          newStruct
-        case other =>
-          throw new IllegalStateException(s"`UpdateFields` has incorrect expression: $other.
" +
-            "Please file a bug report with this error message, stack trace, and the query.")
-      }
-  }
-
-  /**
-   * Adds missing fields recursively into given `col` expression, based on the target `StructType`.
-   * This is called by `compareAndAddFields` when we find two struct columns with same name
but
-   * different nested fields. This method will find out the missing nested fields from `col`
to
-   * `target` struct and add these missing nested fields. Currently we don't support finding
out
-   * missing nested fields of struct nested in array or struct nested in map.
-   */
-  private def addFields(col: NamedExpression, target: StructType): Expression = {
+  private def addFields(col: Expression, targetType: StructType): Expression = {
     assert(col.dataType.isInstanceOf[StructType], "Only support StructType.")
 
     val resolver = conf.resolver
-    val missingFieldsOpt =
-      StructType.findMissingFields(col.dataType.asInstanceOf[StructType], target, resolver)
-
-    // We need to sort columns in result, because we might add another column in other side.
-    // E.g., we want to union two structs "a int, b long" and "a int, c string".
-    // If we don't sort, we will have "a int, b long, c string" and
-    // "a int, c string, b long", which are not compatible.
-    if (missingFieldsOpt.isEmpty) {
-      sortStructFields(col)
-    } else {
-      missingFieldsOpt.map { s =>
-        val struct = addFieldsInto(col, s.fields)
-        // Combines `WithFields`s to reduce expression tree.
-        val reducedStruct = struct.transformUp(OptimizeUpdateFields.optimizeUpdateFields)
-        val sorted = sortStructFieldsInWithFields(reducedStruct)
-        sorted
-      }.get
+    val colType = col.dataType.asInstanceOf[StructType]
+
+    val newStructFields = mutable.ArrayBuffer.empty[Expression]
+
+    val targetStructFields = targetType.fields.foreach { expectedField =>
+      val currentField = colType.fields.find(f => resolver(f.name, expectedField.name))
+
+      val newExpression = (currentField, expectedField.dataType) match {
+        case (Some(cf), expectedType: StructType) if cf.dataType.isInstanceOf[StructType]
=>
+            val extractedValue = ExtractValue(col, Literal(cf.name), resolver)
+            val combinedStruct = addFields(extractedValue, expectedType)
+            if (extractedValue.nullable) {
+              If(IsNull(extractedValue),
+                Literal(null, combinedStruct.dataType),
+                combinedStruct)
+            } else {
+              combinedStruct
+            }
+        case (Some(cf), _) =>
+          ExtractValue(col, Literal(cf.name), resolver)
+        case (None, expectedType) =>
+          Literal(null, expectedType)
+      }
+      newStructFields ++= Literal(expectedField.name) :: newExpression :: Nil
     }
-  }
 
-  /**
-   * Adds missing fields recursively into given `col` expression. The missing fields are
given
-   * in `fields`. For example, given `col` as "z struct<z:int, y:int>, x int", and
`fields` is
-   * "z struct<w:long>, w string". This method will add a nested `z.w` field and a
top-level
-   * `w` field to `col` and fill null values for them. Note that because we might also add
missing
-   * fields at other side of Union, we must make sure corresponding attributes at two sides
have
-   * same field order in structs, so when we adding missing fields, we will sort the fields
based on
-   * field names. So the data type of returned expression will be
-   * "w string, x int, z struct<w:long, y:int, z:int>".
-   */
-  private def addFieldsInto(
-      col: Expression,
-      fields: Seq[StructField]): Expression = {
-    fields.foldLeft(col) { case (currCol, field) =>
-      field.dataType match {
-        case st: StructType =>
-          val resolver = conf.resolver
-          val colField = currCol.dataType.asInstanceOf[StructType]
-            .find(f => resolver(f.name, field.name))
-          if (colField.isEmpty) {
-            // The whole struct is missing. Add a null.
-            UpdateFields(currCol, field.name, Literal(null, st))
-          } else {
-            UpdateFields(currCol, field.name,
-              addFieldsInto(ExtractValue(currCol, Literal(field.name), resolver), st.fields))
-          }
-        case dt =>
-          UpdateFields(currCol, field.name, Literal(null, dt))
+    colType.fields
+      .filter(f => targetType.fields.find(tf => resolver(f.name, tf.name)).isEmpty)
+      .foreach { f =>
+        newStructFields ++= Literal(f.name) :: ExtractValue(col, Literal(f.name), resolver)
:: Nil

Review comment:
       Is this to add fields only in left side at the end of struct? Doesn't it match original
field order?




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