ddl: fix drop index failed when index contain auto_increment column and more than 2 index contain auto_increment_column

ddl/db_change_test.go

@@ -754,6 +754,16 @@ func (s *testStateChangeSuite) TestParallelDropColumn(c *C) {
 	s.testControlParallelExecSQL(c, sql, sql, f)
 }
 
+func (s *testStateChangeSuite) TestParallelDropIndex(c *C) {
+	sql1 := "alter table t drop index idx1 ;"
+	sql2 := "alter table t drop index idx2 ;"
+	f := func(c *C, err1, err2 error) {
+		c.Assert(err1, IsNil)
+		c.Assert(err2.Error(), Equals, "[autoid:1075]Incorrect table definition; there can be only one auto column and it must be defined as a key")
+	}
+	s.testControlParallelExecSQL(c, sql1, sql2, f)
+}
+
 func (s *testStateChangeSuite) TestParallelCreateAndRename(c *C) {
 	sql1 := "create table t_exists(c int);"
 	sql2 := "alter table t rename to t_exists;"
@@ -770,7 +780,7 @@ type checkRet func(c *C, err1, err2 error)
 func (s *testStateChangeSuite) testControlParallelExecSQL(c *C, sql1, sql2 string, f checkRet) {
 	_, err := s.se.Execute(context.Background(), "use test_db_state")
 	c.Assert(err, IsNil)
-	_, err = s.se.Execute(context.Background(), "create table t(a int, b int, c int)")
+	_, err = s.se.Execute(context.Background(), "create table t(a int, b int, c int, d int auto_increment,e int, index idx1(d), index idx2(d,e))")
 	c.Assert(err, IsNil)
 	defer s.se.Execute(context.Background(), "drop table t")
 

ddl/ddl_api.go

@@ -3396,11 +3396,10 @@ func (d *ddl) DropIndex(ctx sessionctx.Context, ti ast.Ident, indexName model.CI
 		return err
 	}
 
-	cols := t.Cols()
-	for _, idxCol := range indexInfo.Columns {
-		if mysql.HasAutoIncrementFlag(cols[idxCol.Offset].Flag) {
-			return autoid.ErrWrongAutoKey
-		}
+	// Check for drop index on auto_increment column.
+	err = checkDropIndexOnAutoIncrementColumn(t.Meta(), indexInfo)
+	if err != nil {
+		return errors.Trace(err)
 	}
 
 	job := &model.Job{

ddl/index.go

@@ -30,6 +30,7 @@ import (
 	"github.com/pingcap/tidb/infoschema"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/meta"
+	"github.com/pingcap/tidb/meta/autoid"
 	"github.com/pingcap/tidb/metrics"
 	"github.com/pingcap/tidb/sessionctx"
 	"github.com/pingcap/tidb/sessionctx/variable"
@@ -465,9 +466,40 @@ func checkDropIndex(t *meta.Meta, job *model.Job) (*model.TableInfo, *model.Inde
 		job.State = model.JobStateCancelled
 		return nil, nil, ErrCantDropFieldOrKey.GenWithStack("index %s doesn't exist", indexName)
 	}
+
+	// Double check for drop index on auto_increment column.
+	err = checkDropIndexOnAutoIncrementColumn(tblInfo, indexInfo)
+	if err != nil {
+		job.State = model.JobStateCancelled
+		return nil, nil, autoid.ErrWrongAutoKey
+	}
+
 	return tblInfo, indexInfo, nil
 }
 
+func checkDropIndexOnAutoIncrementColumn(tblInfo *model.TableInfo, indexInfo *model.IndexInfo) error {
+	cols := tblInfo.Columns
+	for _, idxCol := range indexInfo.Columns {
+		if !mysql.HasAutoIncrementFlag(cols[idxCol.Offset].Flag) {
+			continue
+		}
+		// check the count of index on auto_increment column.
+		count := 0
+		for _, idx := range tblInfo.Indices {
+			for _, c := range idx.Columns {
+				if c.Name.L == idxCol.Name.L {
+					count++
+					break
+				}
+			}
+		}
+		if count < 2 {
+			return autoid.ErrWrongAutoKey
+		}
+	}
+	return nil
+}
+
 func checkRenameIndex(t *meta.Meta, job *model.Job) (*model.TableInfo, model.CIStr, model.CIStr, error) {
 	var from, to model.CIStr
 	schemaID := job.SchemaID