Rework fix for #8290: Unique scan is incorrectly reported in the explained plan for unique index and IS NULL predicate

Author: dyemanov

src/jrd/btr.cpp

@@ -6769,7 +6769,7 @@ static bool scan(thread_db* tdbb, UCHAR* pointer, RecordBitmap** bitmap, RecordB
 	const bool partUpper = (retrieval->irb_upper_count < idx->idx_count);
 
 	// Reset flags this routine does not check in the loop below
-	flag &= ~(irb_equality | irb_ignore_null_value_key | irb_root_list_scan);
+	flag &= ~(irb_equality | irb_unique | irb_ignore_null_value_key | irb_root_list_scan);
 	flag &= ~(irb_exclude_lower | irb_exclude_upper);
 
 	IndexNode node;

src/jrd/btr.h

@@ -237,6 +237,7 @@ const int irb_exclude_lower	= 32;			// exclude lower bound keys while scanning i
 const int irb_exclude_upper	= 64;			// exclude upper bound keys while scanning index
 const int irb_multi_starting	= 128;		// Use INTL_KEY_MULTI_STARTING
 const int irb_root_list_scan	= 256;		// Locate list items from the root
+const int irb_unique	= 512;				// Unique match (currently used only for plan output)
 
 // Force include flags - always include appropriate key while scanning index
 const int irb_force_lower	= irb_exclude_lower;

src/jrd/optimizer/Retrieval.cpp

@@ -1245,6 +1245,9 @@ InversionNode* Retrieval::makeIndexScanNode(IndexScratch* indexScratch) const
 	// Check to see if this is really an equality retrieval
 	if (retrieval->irb_lower_count == retrieval->irb_upper_count)
 	{
+		const bool fullMatch = (retrieval->irb_lower_count == idx->idx_count);
+		bool uniqueMatch = false;
+
 		retrieval->irb_generic |= irb_equality;
 
 		for (unsigned i = 0; i < retrieval->irb_lower_count; i++)
@@ -1254,7 +1257,22 @@ InversionNode* Retrieval::makeIndexScanNode(IndexScratch* indexScratch) const
 				retrieval->irb_generic &= ~irb_equality;
 				break;
 			}
+
+			if (segments[i].scanType == segmentScanMissing ||
+				segments[i].scanType == segmentScanEquivalent)
+			{
+				if (fullMatch && (idx->idx_flags & idx_primary))
+					uniqueMatch = true;
+			}
+			else if (segments[i].scanType == segmentScanEqual)
+			{
+				if (fullMatch && (idx->idx_flags & idx_unique))
+					uniqueMatch = true;
+			}
 		}
+
+		if ((retrieval->irb_generic & irb_equality) && uniqueMatch)
+			retrieval->irb_generic |= irb_unique;
 	}
 
 	// If we are matching less than the full index, this is a partial match

src/jrd/recsrc/RecordSource.cpp

@@ -203,26 +203,18 @@ void RecordSource::printInversion(thread_db* tdbb, const InversionNode* inversio
 				}
 
 				const index_desc& idx = retrieval->irb_desc;
-				const bool primaryIdx = (idx.idx_flags & idx_primary);
-				const bool uniqueIdx = (idx.idx_flags & idx_unique);
 				const USHORT segCount = idx.idx_count;
 
 				const USHORT minSegs = MIN(retrieval->irb_lower_count, retrieval->irb_upper_count);
 				const USHORT maxSegs = MAX(retrieval->irb_lower_count, retrieval->irb_upper_count);
 
 				const bool equality = (retrieval->irb_generic & irb_equality);
+				const bool unique = (retrieval->irb_generic & irb_unique);
 				const bool partial = (retrieval->irb_generic & irb_partial);
 
 				const bool fullscan = (maxSegs == 0);
 				const bool list = (retrieval->irb_list != nullptr);
 
-				bool unique = false;
-				if (!list && equality && minSegs == segCount)
-				{
-					unique = (retrieval->irb_generic & irb_ignore_null_value_key) ?
-						uniqueIdx : primaryIdx;
-				}
-
 				string bounds;
 				if (!unique && !fullscan)
 				{