[release-1.0]ddl: support the rolling upgrade. (#6301) (#6306)

ddl/ddl_api.go

@@ -1259,7 +1259,16 @@ func (d *ddl) getModifiableColumnJob(ctx context.Context, ident ast.Ident, origi
  }
 
  newCol := table.ToColumn(&model.ColumnInfo{
- ID: col.ID,
+ ID: col.ID,
+ // We use this PR(https://github.com/pingcap/tidb/pull/6274) as the dividing line to define whether it is a new version or an old version TiDB.
+ // The old version TiDB initializes the column's offset and state here.
+ // The new version TiDB doesn't initialize the column's offset and state, and it will do the initialization in run DDL function.
+ // When we do the rolling upgrade the following may happen:
+ // a new version TiDB builds the DDL job that doesn't be set the column's offset and state,
+ // and the old version TiDB is the DDL owner, it doesn't get offset and state from the store. Then it will encounter errors.
+ // So here we set offset and state to support the rolling upgrade.
+ Offset: col.Offset,
+ State: col.State,
  OriginDefaultValue: col.OriginDefaultValue,
  FieldType: *spec.NewColumn.Tp,
  Name: spec.NewColumn.Name.Name,