should fill index data after adding an index on a virtual generated column

[zz-jason]

Bug Report

1. What did you do?

All the following operations are executed on a tidb-server built from #10802

drop table if exists t;
create table t(a bigint, b bigint as (a+1) virtual, c bigint as (b+1) virtual);
alter table t add index idx_b(b);
alter table t add index idx_c(c);
insert into t(a) values(1);
alter table t add column(d bigint as (c+1) virtual);

The query below can produce a correct result:

TiDB(root@127.0.0.1:test) > select * from t where d > 2;
+------+------+------+------+
| a    | b    | c    | d    |
+------+------+------+------+
|    1 |    2 |    3 |    4 |
+------+------+------+------+
1 row in set (0.00 sec)

Then create an index on the newly added column d:

alter table t add index idx_d(d);

And run the query again, the result is incorrect:

TiDB(root@127.0.0.1:test) > select * from t where d > 2;
Empty set (0.00 sec)

The execution plan now is changed to:

TiDB(root@127.0.0.1:test) > desc select * from t where d > 2;
+----------------------+-------+------+----------------------------------------------------------------------------------------------------------------------------------+
| id                   | count | task | operator info                                                                                                                    |
+----------------------+-------+------+----------------------------------------------------------------------------------------------------------------------------------+
| Projection_11        | 0.33  | root | test.t.a, cast(plus(test.t.a, 1)), cast(plus(cast(plus(test.t.a, 1)), 1)), cast(plus(cast(plus(cast(plus(test.t.a, 1)), 1)), 1)) |
| └─IndexLookUp_12     | 0.33  | root |                                                                                                                                  |
|   ├─IndexScan_9      | 0.33  | cop  | table:t, index:d, range:(2,+inf], keep order:false, stats:pseudo                                                                 |
|   └─TableScan_10     | 0.33  | cop  | table:t, keep order:false, stats:pseudo                                                                                          |
+----------------------+-------+------+----------------------------------------------------------------------------------------------------------------------------------+
4 rows in set (0.00 sec)

2. What did you expect to see?

produce the correct result

3. What did you see instead?

As I mentioned above, it produces no result.

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

TiDB(root@127.0.0.1:test) > select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v3.0.0-rc.1-314-gca686bba7
Git Commit Hash: ca686bba759ea6127fae70746abba5437f6c7e42
Git Branch: pr/10802
UTC Build Time: 2019-07-09 02:44:55
GoVersion: go version go1.12.5 darwin/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false
1 row in set (0.00 sec)

[crazycs520]

I will fix this today.

[zz-jason]

I think @tangenta is under investigating?

[crazycs520]

@tangenta is busy doing another thing now.