ddl: use original column name in duplicate column error

[u5surf]

What problem does this PR solve?

fix #9285

What is changed and how it works?

Check List

• Unit test
  OK, I checked following
  https://github.com/pingcap/tidb/blob/master/CONTRIBUTING.md#run-test
• Integration test
  What is integration tests ? and how can I ?
• Manual test (add detailed scripts or steps below)

$mysql -u root -P 4000 -h 127.0.0.1
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.7.10-TiDB-v3.0.0-beta-52-g55da8ad9f MySQL Community Server (Apache License 2.0)

Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| INFORMATION_SCHEMA |
| PERFORMANCE_SCHEMA |
| mysql              |
| test               |
+--------------------+
4 rows in set (0.00 sec)

mysql> use test;
Database changed
mysql> show tables;
Empty set (0.00 sec)

mysql> create table tt( ID123 int , ID123 int );
ERROR 1060 (42S21): Duplicate column name 'ID123'
mysql> create table tt( charID varchar(10) , charID varchar(10) charset utf8mb4);
ERROR 1060 (42S21): Duplicate column name 'charID'
mysql> create table tt( WHYNOTUPPER char , WHYNOTUPPER int);
ERROR 1060 (42S21): Duplicate column name 'WHYNOTUPPER'
mysql>

Code changes

• Has exported function/method change
  no
• Has exported variable/fields change
  no
• Has interface methods change
  no
• Has persistent data change
  no

Side effects

• Possible performance regression
  probably no
• Increased code complexity
  no
• Breaking backward compatibility
  no

Related changes

• Need to cherry-pick to the release branch
  nothing
• Need to update the documentation
  nothing
• Need to update the tidb-ansible repository
  ?
• Need to be included in the release note
  probably nothing??

[CLAassistant]

All committers have signed the CLA.

[xiekeyi98]

Thanks for your contirbution.
I was wondering if you could add some unit test to avoid this error next time?

[codecov-io]

Codecov Report

Merging #9291 into master will increase coverage by <.01%.
The diff coverage is 71.42%.

@@            Coverage Diff             @@
##           master    #9291      +/-   ##
==========================================
+ Coverage   67.16%   67.16%   +<.01%     
==========================================
  Files         371      371              
  Lines       77505    77505              
==========================================
+ Hits        52057    52058       +1     
+ Misses      20794    20793       -1     
  Partials     4654     4654

Impacted Files	Coverage Δ
ddl/ddl_api.go	74.64% <71.42%> (ø)	⬆️
util/systimemon/systime_mon.go	80% <0%> (-20%)	⬇️
executor/distsql.go	73% <0%> (+0.46%)	⬆️
store/tikv/lock_resolver.go	42.65% <0%> (+0.94%)	⬆️

---

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[zz-jason]

Please add some UT to cover this bug.

[u5surf]

i fixed TestFieldCase to check column name case strictly.

before:(if column name includes bigcase character as Field)

PASS: column_test.go:844: testColumnSuite.TestDropColumn	0.192s

----------------------------------------------------------------------
FAIL: column_test.go:960: testColumnSuite.TestFieldCase

column_test.go:975:
    c.Assert(err.Error(), Equals, infoschema.ErrColumnExists.GenWithStackByArgs("Field").Error())
... obtained string = "[schema:1060]Duplicate column name 'field'"
... expected string = "[schema:1060]Duplicate column name 'Field'"


----------------------------------------------------------------------

after: fixed

ok  	github.com/pingcap/tidb/config	0.022s	coverage: 18.9% of statements
ok  	github.com/pingcap/tidb/ddl	48.576s	coverage: 78.6% of statements

[zhouqiang-cl]

/rebuild

[zz-jason]

LGTM

[zz-jason]

/run-all-tests

[zimulala]

LGTM

[zz-jason]

@u5surf Please cherry pick this commit to release 2.1 and release 2.0 branches.