planner: fix index prefix matching

ddl/multi_schema_change_test.go

@@ -719,8 +719,8 @@ func TestMultiSchemaChangeAddDropIndexes(t *testing.T) {
 	tk.MustExec("drop table if exists t;")
 	tk.MustExec("create table t (a int, b int, c int, index (a), index(b), index(c));")
 	tk.MustExec("insert into t values (1, 2, 3);")
-	tk.MustExec("alter table t add index aa(a), drop index a, add index cc(c), drop index b, drop index c, add index bb(b);")
-	tk.MustQuery("select * from t use index(aa, bb, cc);").Check(testkit.Rows("1 2 3"))
+	tk.MustExec("alter table t add index xa(a), drop index a, add index xc(c), drop index b, drop index c, add index xb(b);")
+	tk.MustQuery("select * from t use index(xa, xb, xc);").Check(testkit.Rows("1 2 3"))
 	tk.MustGetErrCode("select * from t use index(a);", errno.ErrKeyDoesNotExist)
 	tk.MustGetErrCode("select * from t use index(b);", errno.ErrKeyDoesNotExist)
 	tk.MustGetErrCode("select * from t use index(c);", errno.ErrKeyDoesNotExist)

planner/core/logical_plan_test.go

@@ -863,7 +863,7 @@ func TestValidate(t *testing.T) {
 			err: ErrUnknownColumn,
 		},
 		{
-			sql: "select * from t t1 use index(e)",
+			sql: "select * from t t1 use index(x)",
 			err: ErrKeyDoesNotExist,
 		},
 		{

planner/core/mock.go

@@ -73,7 +73,7 @@ func MockSignedTable() *model.TableInfo {
 			Unique: true,
 		},
 		{
-			Name: model.NewCIStr("e"),
+			Name: model.NewCIStr("x"),
 			Columns: []*model.IndexColumn{
 				{
 					Name:   model.NewCIStr("e"),

planner/core/planbuilder.go

@@ -1168,7 +1168,8 @@ func (b *PlanBuilder) detectSelectWindow(sel *ast.SelectStmt) bool {
 }
 
 func getPathByIndexName(paths []*util.AccessPath, idxName model.CIStr, tblInfo *model.TableInfo) *util.AccessPath {
-	var primaryIdxPath *util.AccessPath
+	var primaryIdxPath, indexPrefixPath *util.AccessPath
+	prefixMatches := 0
 	for _, path := range paths {
 		if path.StoreType == kv.TiFlash {
 			continue
@@ -1180,10 +1181,19 @@ func getPathByIndexName(paths []*util.AccessPath, idxName model.CIStr, tblInfo *
 		if path.Index.Name.L == idxName.L {
 			return path
 		}
+		if strings.HasPrefix(path.Index.Name.L, idxName.L) {
+			indexPrefixPath = path
+			prefixMatches++
+		}
 	}
 	if isPrimaryIndex(idxName) && tblInfo.HasClusteredIndex() {
 		return primaryIdxPath
 	}
+
+	// Return only unique prefix matches
+	if prefixMatches == 1 {
+		return indexPrefixPath
+	}
 	return nil
 }
 

planner/core/planbuilder_test.go

@@ -91,6 +91,11 @@ func TestGetPathByIndexName(t *testing.T) {
 	require.NotNil(t, path)
 	require.Equal(t, accessPath[1], path)
 
+	// "id" is a prefix of "idx"
+	path = getPathByIndexName(accessPath, model.NewCIStr("id"), tblInfo)
+	require.NotNil(t, path)
+	require.Equal(t, accessPath[1], path)
+
 	path = getPathByIndexName(accessPath, model.NewCIStr("primary"), tblInfo)
 	require.NotNil(t, path)
 	require.Equal(t, accessPath[0], path)