ddl: fix add unique index on partitioned table (by RANGE COLUMNS) failed

[lonng]

Signed-off-by: Lonng heng@lonng.org

What problem does this PR solve?

create table t(
    a int,
    b varchar(100),
    c int,
    INDEX idx_c(c))
PARTITION BY RANGE COLUMNS( a ) (
    PARTITION p0 VALUES LESS THAN (6),
    PARTITION p1 VALUES LESS THAN (11),
    PARTITION p2 VALUES LESS THAN (16),
    PARTITION p3 VALUES LESS THAN (21)
);

mysql> alter table t add unique index idx_a(a);
ERROR 1105 (HY000): line 1 column 7 near ""

What is changed and how it works?

The Expr field in PartitionInfo is not always be assigned a value (e.g: PARTITION BY RANGE COLUMNS(...)).
This PR use columns in PartitionInfo directly if the PartitionInfo.Expr is an empty string.

Check List

Tests

• Unit test
• Manual test (add detailed scripts or steps below)

Related changes

• Need to cherry-pick to the release branch

Release note

• Fix add unique index on the partitioned table (by RANGE COLUMNS(...)) failed.

[lonng]

/run-all-tests

[codecov]

Codecov Report

Merging #11946 into master will decrease coverage by 0.1333%.
The diff coverage is 76.4705%.

@@               Coverage Diff                @@
##             master     #11946        +/-   ##
================================================
- Coverage   81.3468%   81.2134%   -0.1334%     
================================================
  Files           443        443                
  Lines         95035      95015        -20     
================================================
- Hits          77308      77165       -143     
- Misses        12267      12356        +89     
- Partials       5460       5494        +34

[tiancaiamao]

LGTM

[zimulala]

LGTM

[crazycs520]

LGTM

[sre-bot]

/run-all-tests

[sre-bot]

cherry pick to release-3.0 failed

[lonng]

Cherry-pick to release-3.0 after #11954 merged

[you06]

/run-cherry-picker

[sre-bot]

cherry pick to release-3.0 in PR #11958