ddl: fix admin check bug

[crazycs520]

What problem does this PR solve?

Use to executed below sqls will error:

drop table if exists t1;
CREATE TABLE t1 (c2 BOOL, PRIMARY KEY (c2));
INSERT INTO t1 SET c2 = '0';
ALTER TABLE t1 ADD COLUMN c3 DATETIME NULL DEFAULT '2668-02-03 17:19:31';
ALTER TABLE t1 ADD INDEX idx3 (c3);
ALTER TABLE t1 ADD COLUMN c4 bit(10) default 127;
ALTER TABLE t1 ADD INDEX idx4 (c4);
ALTER TABLE t1 ADD COLUMN c5 SET('a', 'b', 'c', 'd') default 'a';
ALTER TABLE t1 ADD INDEX idx5(c5);
admin check table t1;

(1105, 't1 err:[admin:1]index:&admin.RecordData{Handle:0, Values:[]types.Datum{types.Datum{k:0xd, collation:0x0, decimal:0x0, length:0x0, i:2440818046768513024, b:[]uint8(nil), x:types.Time{Time:types.MysqlTime{year:0xa6c, month:0x2, day:0x3, hour:17, minute:0x13, second:0x1f, microsecond:0x0}, Type:0xc, Fsp:0}}}} != record:&admin.RecordData{Handle:0, Values:[]types.Datum{types.Datum{k:0xd, collation:0x0, decimal:0x0, length:0x0, i:0, b:[]uint8(nil), x:types.Time{Time:types.MysqlTime{year:0xa6c, month:0x2, day:0x3, hour:17, minute:0x13, second:0x1f, microsecond:0x0}, Type:0xc, Fsp:0}}}}')

The bug is:
When tablecodec.unflatten() the datetime type, the flatten value still in datum.i,
we have to clear the flatten value to make sure a flatten datum go through unflatten is deep equal the origin datum

What is changed and how it works?

Check List

Tests

• Unit test

[winkyao]

LGTM

[winkyao]

@crazycs520 Please posts the error information in the description, and explain why your fix work.

[breezewish]

Is it needed to clear other fields in datum as well, for example, field b?

[shenli]

Will this bug affect other parts except for AdminCheck?

[crazycs520]

@shenli yes, It will affect other parts too.
em...
I mean the change will affect other parts.

[winkyao]

@shenli No, it just affects the admin check table.

[crazycs520]

@zimulala @ciscoxll PTAL

[shenli]

/run-all-tests

[shenli]

unflatten is a fundamental function. Is it a bug?

[crazycs520]

@shenli the flatten and unflatten code use to be:

// for datetime
// origin
data1 := Datum{
    i:0,
    x: Time{
        ...
    },
    ...
}
// after flatten
data2 := Datum{
    i:2440818046768513024,
    x: nil,
    ...
}

// after unflatten
data3 := Datum{
    i:2440818046768513024,
     x: Time{
        ...
    },
    ...
}

admin check will compare datum then found datum.i not equal, then return error.
Maybe this is not exactly a bug. Because data3.GetMysqlTime() still return right result.
if use datum.CompareDatum() to compare in admin check, then do not change the unflatten function.

[shenli]

Do we need to clean the i for TypeDuration?

[crazycs520]

No, we needn't. d.SetMysqlDuration(x) will set i again.

[zhexuany]

@crazycs520 SetDuration -> SetMysqlDuration. Inside SetMysqlDuration, we assign the value of duration to i after type conversion. So we definitely need clean i of Datum in the case of TypeDuration.

[shenli]

@coocood PTAL

[crazycs520]

@breeswish Sorry, I didn’t see yours comment before.
In flatten and unflatten, I think we can only care about i.

[zz-jason]

@crazycs520 Seems like we need to clear other fields when we call Datum.SetXXXX ?

[crazycs520]

@coocood What is your opinion?

[ciscoxll]

/run-all-tests

[crazycs520]

/run-all-tests

[coocood]

LGTM

[zhexuany]

cc @crazycs520 please fix ci failure.

[alivxxx]

@zhexuany It will be fixed in #7434

[coocood]

/run-unit-test

[crazycs520]

/run-all-tests

[shenli]

LGTM