Merge pull request cockroachdb#6380 from RaduBerinde/fix-singlekey-opt

sql: fix single-key optimization bug

Author: RaduBerinde

sql/index_selection.go

@@ -219,11 +219,14 @@ func selectIndex(
 	}
 
 	// If we have no filter, we can request a single key in some cases.
-	if noFilter && analyzeOrdering != nil {
+	if noFilter && analyzeOrdering != nil && s.isSecondaryIndex {
 		_, _, singleKey := analyzeOrdering(plan.Ordering())
 		if singleKey {
-			s.spans = s.spans[:1]
-			s.spans[0].count = 1
+			// We only need to retrieve one key, but some spans might contain no
+			// keys so we need to keep all of them.
+			for i := range s.spans {
+				s.spans[i].count = 1
+			}
 		}
 	}
 
@@ -412,8 +415,8 @@ func (v *indexInfo) analyzeOrdering(scan *scanNode, analyzeOrdering analyzeOrder
 	}
 
 	if log.V(2) {
-		log.Infof("%s: analyzeOrdering: weight=%0.2f reverse=%v index=%d",
-			v.index.Name, weight, v.reverse, fwdIndexOrdering)
+		log.Infof("%s: analyzeOrdering: weight=%0.2f reverse=%v match=%d",
+			v.index.Name, weight, v.reverse, match)
 	}
 }
 

sql/testdata/aggregate

@@ -399,6 +399,13 @@ CREATE TABLE abc (
 statement ok
 INSERT INTO abc VALUES ('one', 1.5, true, 5::decimal), ('two', 2.0, false, 1.1::decimal)
 
+# Verify we don't try to apply the single-key optimization to the primary index.
+query ITT
+EXPLAIN SELECT MIN(a) FROM abc
+----
+0 group MIN(a)
+1 scan  abc@primary -
+
 query TRBR
 SELECT MIN(a), MIN(b), MIN(c), MIN(d) FROM abc
 ----
@@ -455,6 +462,17 @@ EXPLAIN SELECT MIN(x) FROM xyz
 0 group MIN(x)
 1 scan  xyz@xy 1:-
 
+query I
+SELECT MIN(x) FROM xyz WHERE x in (0, 4, 7)
+----
+4
+
+query ITT
+EXPLAIN SELECT MIN(x) FROM xyz WHERE x in (0, 4, 7)
+----
+0 group MIN(x)
+1 scan  xyz@xy 1:/0-/1 1:/4-/5 1:/7-/8
+
 query I
 SELECT MAX(x) FROM xyz
 ----