ddl: fix panic when add index of generated column. (#8620)

.travis.yml

@@ -3,7 +3,7 @@ language: go
 go_import_path: github.com/pingcap/tidb
 
 go:
-  - "1.11"
+  - "1.11.3"
 
 env:
     - TRAVIS_COVERAGE=0

circle.yml

@@ -3,7 +3,7 @@ version: 2
 jobs:
   build:
     docker:
-      - image: golang:1.11
+      - image: golang:1.11.3
     working_directory: /go/src/github.com/pingcap/tidb
     steps:
       - checkout

ddl/db_integration_test.go

@@ -152,6 +152,24 @@ func (s *testIntegrationSuite) TestEndIncluded(c *C) {
 	tk.MustExec("admin check table t")
 }
 
+func (s *testIntegrationSuite) TestNullGeneratedColumn(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("CREATE TABLE `t` (" +
+		"`a` int(11) DEFAULT NULL," +
+		"`b` int(11) DEFAULT NULL," +
+		"`c` int(11) GENERATED ALWAYS AS (`a` + `b`) VIRTUAL DEFAULT NULL," +
+		"`h` varchar(10) DEFAULT NULL," +
+		"`m` int(11) DEFAULT NULL" +
+		") ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin")
+
+	tk.MustExec("insert into t values()")
+	tk.MustExec("alter table t add index idx_c(c)")
+	tk.MustExec("drop table t")
+}
+
 func (s *testIntegrationSuite) TestCaseInsensitiveCharsetAndCollate(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 

ddl/index.go

@@ -456,7 +456,7 @@ type addIndexWorker struct {
 	defaultVals        []types.Datum
 	idxRecords         []*indexRecord
 	rowMap             map[int64]types.Datum
-	rowDecoder         decoder.RowDecoder
+	rowDecoder         *decoder.RowDecoder
 	idxKeyBufs         [][]byte
 	batchCheckKeys     []kv.Key
 	distinctCheckFlags []bool
@@ -542,8 +542,8 @@ func (w *addIndexWorker) getIndexRecord(handle int64, recordKey []byte, rawRecor
 			}
 			continue
 		}
-		idxColumnVal := w.rowMap[col.ID]
-		if _, ok := w.rowMap[col.ID]; ok {
+		idxColumnVal, ok := w.rowMap[col.ID]
+		if ok {
 			idxVal[j] = idxColumnVal
 			// Make sure there is no dirty data.
 			delete(w.rowMap, col.ID)
@@ -566,10 +566,19 @@ func (w *addIndexWorker) getIndexRecord(handle int64, recordKey []byte, rawRecor
 		}
 		idxVal[j] = idxColumnVal
 	}
+	// If there are generated column, rowDecoder will use column value that not in idxInfo.Columns to calculate
+	// the generated value, so we need to clear up the reusing map.
+	w.cleanRowMap()
 	idxRecord := &indexRecord{handle: handle, key: recordKey, vals: idxVal}
 	return idxRecord, nil
 }
 
+func (w *addIndexWorker) cleanRowMap() {
+	for id := range w.rowMap {
+		delete(w.rowMap, id)
+	}
+}
+
 // getNextHandle gets next handle of entry that we are going to process.
 func (w *addIndexWorker) getNextHandle(taskRange reorgIndexTask, taskDone bool) (nextHandle int64) {
 	if !taskDone {
@@ -788,6 +797,7 @@ func (w *addIndexWorker) handleBackfillTask(d *ddlCtx, task *reorgIndexTask) *ad
 			// we should check whether this ddl job is still runnable.
 			err = w.ddlWorker.isReorgRunnable(d)
 		}
+
 		if err != nil {
 			result.err = err
 			return result

executor/executor.go

@@ -410,7 +410,7 @@ type CheckTableExec struct {
 	done   bool
 	is     infoschema.InfoSchema
 
-	genExprs map[string]expression.Expression
+	genExprs map[model.TableColumnID]expression.Expression
 }
 
 // Open implements the Executor Open interface.

model/model.go

@@ -15,7 +15,6 @@ package model
 
 import (
 	"encoding/json"
-	"fmt"
 	"strings"
 	"time"
 
@@ -556,7 +555,8 @@ func collationToProto(c string) int32 {
 	return int32(mysql.DefaultCollationID)
 }
 
-// GetTableColumnID gets a ID of a column with table ID
-func GetTableColumnID(tableInfo *TableInfo, col *ColumnInfo) string {
-	return fmt.Sprintf("%d_%d", tableInfo.ID, col.ID)
+// TableColumnID is composed by table ID and column ID.
+type TableColumnID struct {
+	TableID  int64
+	ColumnID int64
 }

planner/core/common_plans.go

@@ -73,7 +73,7 @@ type CheckTable struct {
 
 	Tables []*ast.TableName
 
-	GenExprs map[string]expression.Expression
+	GenExprs map[model.TableColumnID]expression.Expression
 }
 
 // RecoverIndex is used for backfilling corrupted index data.

planner/core/planbuilder.go

@@ -32,7 +32,6 @@ import (
 	"github.com/pingcap/tidb/table"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/types/parser_driver"
-	"github.com/pingcap/tidb/util/admin"
 	"github.com/pingcap/tidb/util/ranger"
 )
 
@@ -530,7 +529,7 @@ func (b *planBuilder) buildAdmin(as *ast.AdminStmt) (Plan, error) {
 
 func (b *planBuilder) buildAdminCheckTable(as *ast.AdminStmt) (*CheckTable, error) {
 	p := &CheckTable{Tables: as.Tables}
-	p.GenExprs = make(map[string]expression.Expression)
+	p.GenExprs = make(map[model.TableColumnID]expression.Expression, len(p.Tables))
 
 	mockTablePlan := LogicalTableDual{}.init(b.ctx)
 	for _, tbl := range p.Tables {
@@ -562,8 +561,7 @@ func (b *planBuilder) buildAdminCheckTable(as *ast.AdminStmt) (*CheckTable, erro
 				return nil, errors.Trace(err)
 			}
 			expr = expression.BuildCastFunction(b.ctx, expr, colExpr.GetType())
-			genColumnName := admin.GetTableColumnID(tableInfo, column.ColumnInfo)
-			p.GenExprs[genColumnName] = expr
+			p.GenExprs[model.TableColumnID{TableID: tableInfo.ID, ColumnID: column.ColumnInfo.ID}] = expr
 		}
 	}
 	return p, nil

tablecodec/tablecodec.go

@@ -305,10 +305,10 @@ func DecodeRowWithMap(b []byte, cols map[int64]*types.FieldType, loc *time.Locat
 		row = make(map[int64]types.Datum, len(cols))
 	}
 	if b == nil {
-		return nil, nil
+		return row, nil
 	}
 	if len(b) == 1 && b[0] == codec.NilFlag {
-		return nil, nil
+		return row, nil
 	}
 	cnt := 0
 	var (

tablecodec/tablecodec_test.go

@@ -137,7 +137,7 @@ func (s *testTableCodecSuite) TestRowCodec(c *C) {
 
 	r, err = DecodeRow(bs, colMap, time.UTC)
 	c.Assert(err, IsNil)
-	c.Assert(r, IsNil)
+	c.Assert(len(r), Equals, 0)
 }
 
 func (s *testTableCodecSuite) TestTimeCodec(c *C) {