ddl: fix potential wrong column definition when setting default value

ddl/column.go

@@ -1774,7 +1774,18 @@ func updateColumnDefaultValue(d *ddlCtx, t *meta.Meta, job *model.Job, newCol *m
 	// The newCol's offset may be the value of the old schema version, so we can't use newCol directly.
 	oldCol.DefaultValue = newCol.DefaultValue
 	oldCol.DefaultValueBit = newCol.DefaultValueBit
-	oldCol.SetFlag(newCol.GetFlag())
+	oldCol.DefaultIsExpr = newCol.DefaultIsExpr
+	if mysql.HasNoDefaultValueFlag(newCol.GetFlag()) {
+		oldCol.AddFlag(mysql.NoDefaultValueFlag)
+	} else {
+		oldCol.DelFlag(mysql.NoDefaultValueFlag)
+		sctx := newContext(d.store)
+		err = checkDefaultValue(sctx, table.ToColumn(oldCol), true)
+		if err != nil {
+			job.State = model.JobStateCancelled
+			return ver, err
+		}
+	}
 
 	ver, err = updateVersionAndTableInfo(d, t, job, tblInfo, true)
 	if err != nil {

ddl/db_change_test.go

@@ -2092,3 +2092,60 @@ func TestParallelRenameTable(t *testing.T) {
 	require.True(t, strings.Contains(checkErr.Error(), "Table 'test.t' doesn't exist"), checkErr.Error())
 	tk.MustExec("rename table tt to t")
 }
+
+func TestConcurrentSetDefaultValue(t *testing.T) {
+	store, dom, clean := testkit.CreateMockStoreAndDomain(t)
+	defer clean()
+
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t(a YEAR NULL DEFAULT '2029')")
+
+	tk1 := testkit.NewTestKit(t, store)
+	tk1.MustExec("use test")
+
+	setdefaultSQL := []string{
+		"alter table t alter a SET DEFAULT '2098'",
+		"alter table t alter a SET DEFAULT '1'",
+	}
+	setdefaultSQLOffset := 0
+
+	var wg sync.WaitGroup
+	d := dom.DDL()
+	originalCallback := d.GetHook()
+	defer d.SetHook(originalCallback)
+	callback := &ddl.TestDDLCallback{Do: dom}
+	skip := false
+	callback.OnJobRunBeforeExported = func(job *model.Job) {
+		switch job.SchemaState {
+		case model.StateDeleteOnly:
+			if skip {
+				break
+			}
+			skip = true
+			wg.Add(1)
+			go func() {
+				_, err := tk1.Exec(setdefaultSQL[setdefaultSQLOffset])
+				if setdefaultSQLOffset == 0 {
+					require.Nil(t, err)
+				}
+				wg.Done()
+			}()
+		}
+	}
+
+	d.SetHook(callback)
+	tk.MustExec("alter table t modify column a MEDIUMINT NULL DEFAULT '-8145111'")
+
+	wg.Wait()
+	tk.MustQuery("select column_type from information_schema.columns where table_name = 't' and table_schema = 'test';").Check(testkit.Rows("mediumint(9)"))
+
+	tk.MustExec("drop table t")
+	tk.MustExec("create table t(a int default 2)")
+	skip = false
+	setdefaultSQLOffset = 1
+	tk.MustExec("alter table t modify column a TIMESTAMP NULL DEFAULT '2017-08-06 10:47:11'")
+	wg.Wait()
+	tk.MustExec("show create table t")
+	tk.MustExec("insert into t value()")
+}