length result is wrong after modify column length

[zimulala]

Description

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

create table t(a int, b binary(22));
insert into t set b='test';
alter table t modify b binary(33);
insert into t set b='test1';
select length(b) from t;

2. What did you expect to see?

+-----------+
| length(b) |
+-----------+
|        33 |
|        33 |
+-----------+

3. What did you see instead?

+-----------+
| length(b) |
+-----------+
|        22 |
|        33 |
+-----------+

4. What version of TiDB are you using (tidb-server -V)?

SIG slack channel

#sig-exec

Score

• 300

Mentor

• @qw4990

[zz-jason]

related issue: #3660

[morgo]

Confirming that I can still reproduce this:

mysql> select length(b) from t;
+-----------+
| length(b) |
+-----------+
|        22 |
|        33 |
+-----------+
2 rows in set (0.00 sec)

mysql> SELECT tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v3.0.0-beta-256-g961f0d235-dirty
Git Commit Hash: 961f0d23514c6ab033a76b2f64c20c87d46e7fdf
Git Branch: fix-idle-connections
UTC Build Time: 2019-03-21 02:33:13
GoVersion: go version go1.12.1 linux/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)

[williamxiongwei]

/pick-up

[ti-challenge-bot]

Pick up success.

[ti-challenge-bot]

@williamxiongwei You did not submit PR within 7 days, so give up automatically.

[ou-bing]

/pick-up

[ti-challenge-bot]

Pick up success.

[wjhuang2016]

If column type change is not enabled, we can't append the padding 0x00 in the end. So I think we should forbid this alter table job.

[ou-bing]

If column type change is not enabled, we can't append the padding 0x00 in the end. So I think we should forbid this alter table job.

Do you think that changing the column type from binary (22) to binary (33) should not be supported?

[wjhuang2016]

If column type change is not enabled, we can't append the padding 0x00 in the end. So I think we should forbid this alter table job.

Do you think that changing the column type from binary (22) to binary (33) should not be supported?

Yeah

[ti-challenge-bot]

@ou-bing You did not submit PR within 7 days, so give up automatically.

[jianzhiyao]

If column type change is not enabled, we can't append the padding 0x00 in the end. So I think we should forbid this alter table job.

Do you think that changing the column type from binary (22) to binary (33) should not be supported?

Yeah

What's the final conclusion?

[wjhuang2016]

@jianzhiyao We shouldn't allow this alter for now.

[LENSHOOD]

Let me do this?

The issue could be easy to fix since modify column feature almost finished.

We can just forbid alter binary to binary when tidb_enable_change_column_type = 0 and do the column change when tidb_enable_change_column_type = 1.

[ti-srebot]

Please edit this comment or add a new comment to complete the following information

Not a bug

1. Remove the 'type/bug' label
2. Add notes to indicate why it is not a bug

Duplicate bug

1. Add the 'type/duplicate' label
2. Add the link to the original bug

Bug

Note: Make Sure that 'component', and 'severity' labels are added
Example for how to fill out the template: #20100

1. Root Cause Analysis (RCA) (optional)

2. Symptom (optional)

3. All Trigger Conditions (optional)

4. Workaround (optional)

5. Affected versions

6. Fixed versions