HIVE-26355: Column compare should be case insensitive for name

[wecharyu]

What changes were proposed in this pull request?

Fix a bug in comparing column fields between old table and new table.

Why are the changes needed?

Hive is case-insensitive in field name, but some engines are case-sensitive, so when calling alter_table the existing column name may not be equal because of the case.

Does this PR introduce any user-facing change?

No

How was this patch tested?

We add two unit tests, can be run with command:

$ mvn test -Dtest=org.apache.hadoop.hive.metastore.utils.TestMetaStoreServerUtils -pl :hive-standalone-metastore-server

[wecharyu]

@pvary @nrg4878 : Could you review this PR?

[pvary]

Maybe we should convert the incoming column names "immediately" to lower case, otherwise other methods like (arePrefixColumns) would suffer from the same comparison issue. What do you think?

[wecharyu]

I have also considered to convert the column names at the top method like alter_table, but since there are only two methods (areSameColumns and arePrefixColumns) that will take use of the compare of names, so I made the conversion in these two methods.

[pvary]

I have also considered to convert the column names at the top method like alter_table, but since there are only two methods (areSameColumns and arePrefixColumns) that will take use of the compare of names, so I made the conversion in these two methods.

Could you please add a javadoc which describes that the methods are case independent?

[wecharyu]

Could you please add a javadoc which describes that the methods are case independent?

Done.