From 2fc18bfe06224ec5014669fb92ea151f0c76350b Mon Sep 17 00:00:00 2001
From: Clint Wylie <cwylie@apache.org>
Date: Fri, 23 Feb 2024 12:40:43 -0800
Subject: [PATCH] fix bug with expression virtual column indexes on missing
 columns for expressions that turn null values into not null values

---
 .../java/org/apache/druid/math/expr/Expr.java     |  5 +++++
 .../druid/segment/filter/BaseFilterTest.java      |  1 +
 .../druid/segment/filter/EqualityFilterTests.java | 15 +++++++++++++++
 3 files changed, 21 insertions(+)

diff --git a/processing/src/main/java/org/apache/druid/math/expr/Expr.java b/processing/src/main/java/org/apache/druid/math/expr/Expr.java
index d118bf475b88..43d669081c06 100644
--- a/processing/src/main/java/org/apache/druid/math/expr/Expr.java
+++ b/processing/src/main/java/org/apache/druid/math/expr/Expr.java
@@ -207,6 +207,11 @@ default ColumnIndexSupplier asColumnIndexSupplier(
 
       final ColumnIndexSupplier delegateIndexSupplier = columnIndexSelector.getIndexSupplier(column);
       if (delegateIndexSupplier == null) {
+        // if the column doesn't exist, check to see if the expression evaluates to a non-null result... if so, we might
+        // need to make a value matcher anyway
+        if (eval(InputBindings.nilBindings()).valueOrDefault() != null) {
+          return NoIndexesColumnIndexSupplier.getInstance();
+        }
         return null;
       }
       final DictionaryEncodedValueIndex<?> delegateRawIndex = delegateIndexSupplier.as(
diff --git a/processing/src/test/java/org/apache/druid/segment/filter/BaseFilterTest.java b/processing/src/test/java/org/apache/druid/segment/filter/BaseFilterTest.java
index f4ecad4485bc..a907bc7cd02d 100644
--- a/processing/src/test/java/org/apache/druid/segment/filter/BaseFilterTest.java
+++ b/processing/src/test/java/org/apache/druid/segment/filter/BaseFilterTest.java
@@ -152,6 +152,7 @@ public abstract class BaseFilterTest extends InitializedNullHandlingTest
           new ExpressionVirtualColumn("vdim3-concat", "dim3 + dim3", ColumnType.LONG, TestExprMacroTable.INSTANCE),
           new ExpressionVirtualColumn("vdim2-offset", "array_offset(dim2, 1)", ColumnType.STRING, TestExprMacroTable.INSTANCE),
           new ExpressionVirtualColumn("nestedArrayLong", "array(arrayLong)", ColumnType.ofArray(ColumnType.LONG_ARRAY), TestExprMacroTable.INSTANCE),
+          new ExpressionVirtualColumn("fake-nvl", "nvl(fake, 'hello')", ColumnType.STRING, TestExprMacroTable.INSTANCE),
           new ListFilteredVirtualColumn("allow-dim0", DefaultDimensionSpec.of("dim0"), ImmutableSet.of("3", "4"), true),
           new ListFilteredVirtualColumn("deny-dim0", DefaultDimensionSpec.of("dim0"), ImmutableSet.of("3", "4"), false),
           new ListFilteredVirtualColumn("allow-dim2", DefaultDimensionSpec.of("dim2"), ImmutableSet.of("a"), true),
diff --git a/processing/src/test/java/org/apache/druid/segment/filter/EqualityFilterTests.java b/processing/src/test/java/org/apache/druid/segment/filter/EqualityFilterTests.java
index 9c2bd90071c5..78b40ea43d7d 100644
--- a/processing/src/test/java/org/apache/druid/segment/filter/EqualityFilterTests.java
+++ b/processing/src/test/java/org/apache/druid/segment/filter/EqualityFilterTests.java
@@ -124,6 +124,7 @@ public void testSingleValueVirtualStringColumnWithoutNulls()
       assertFilterMatches(new EqualityFilter("vdim0", ColumnType.LONG, 1L, null), ImmutableList.of("1"));
     }
 
+
     @Test
     public void testListFilteredVirtualColumn()
     {
@@ -407,6 +408,20 @@ public void testSingleValueVirtualStringColumnWithNulls()
       }
     }
 
+
+    @Test
+    public void testSingleValueVirtualStringColumnMissingColumnCoalesce()
+    {
+      assertFilterMatches(
+          new EqualityFilter("fake-nvl", ColumnType.STRING, "0", null),
+          ImmutableList.of()
+      );
+      assertFilterMatches(
+          new EqualityFilter("fake-nvl", ColumnType.STRING, "hello", null),
+          ImmutableList.of("0", "1", "2", "3", "4", "5")
+      );
+    }
+
     @Test
     public void testMultiValueStringColumn()
     {