sql/analyzer/indexed_joins.go: Use partial indexes for indexed joins when a full index isn't available.

enginetest/query_plans.go

@@ -262,6 +262,15 @@ var PlanTests = []QueryPlanTest{
 			"     └─ IndexedTableAccess(othertable on [othertable.i2])\n" +
 			"",
 	},
+	{
+		Query: "SELECT /*+ JOIN_ORDER(mt, o) */ * FROM mytable mt INNER JOIN one_pk o ON mt.i = o.pk AND mt.s = o.c2",
+		ExpectedPlan: "IndexedJoin(mt.i = o.pk AND mt.s = o.c2)\n" +
+			" ├─ TableAlias(mt)\n" +
+			" │   └─ Table(mytable)\n" +
+			" └─ TableAlias(o)\n" +
+			"     └─ IndexedTableAccess(one_pk on [one_pk.pk])\n" +
+			"",
+	},
 	{
 		Query: "SELECT i, i2, s2 FROM mytable RIGHT JOIN othertable ON i = i2 - 1",
 		ExpectedPlan: "Project(mytable.i, othertable.i2, othertable.s2)\n" +

sql/analyzer/indexed_joins.go

@@ -681,7 +681,19 @@ func getJoinIndex(
 	exprsByTable := joinExprsByTable(joinCondPredicates)
 	indexesByTable := make(joinIndexesByTable)
 	for table, cols := range exprsByTable {
-		idx := ia.IndexByExpression(ctx, ctx.GetCurrentDatabase(), normalizeExpressions(tableAliases, extractExpressions(cols)...)...)
+		exprs := extractExpressions(cols)
+		idx := ia.IndexByExpression(ctx, ctx.GetCurrentDatabase(), normalizeExpressions(tableAliases, exprs...)...)
+		// If we do not find a perfect index, we take the first single column partial index if there is one.
+		// This currently only finds single column indexes. A better search would look for the most complete
+		// index available, covering the columns with the most specificity / highest cardinality.
+		if idx == nil && len(exprs) > 1 {
+			for _, e := range exprs {
+				idx = ia.IndexByExpression(ctx, ctx.GetCurrentDatabase(), normalizeExpressions(tableAliases, e)...)
+				if idx != nil {
+					break
+				}
+			}
+		}
 		indexesByTable[table] = append(indexesByTable[table], colExprsToJoinIndex(table, idx, joinCond, cols))
 	}