Fix CORE-3078 bug

[dmitriy-volkov]

Overview

On PostgreSQL, the dropDefaultValue command only sets the default value to NULL rather than actually dropping it.

Looking at DropDefaultValueGenerator.java, there's no mention of PostgreSQL anywhere, so it ends up using the default "SET DEFAULT NULL".

Steps to Reproduce

1. Create a table with an int column containing a default value of 10
2. Run a changeLog with for that column
3. \d describe that table to see that it now has a default value of null

Expected Results

\d describe that table to see that it has no default value.

[SteveDonie]

Thanks for the pull request! We are currently very close to shipping version 3.8.1, and will evaluate your contribution for inclusion in the next release.

[dmitriy-volkov]

@SteveDonie any estimates on when this can be merged?

[ro-rah]

Hi @dmitriy-volkov !

Again thanks for the PR and your time!
We have been streamlining our internal PR acceptance process and can move this to the next state (Conditioning) easier if you include tests (unit and/or integration)

Would you be able to make update corresponding test:
liquibase-core/src/test/java/liquibase/sqlgenerator/core/DropDefaultValueGeneratorTest.java

Thanks,

Ronak

[ro-rah]

Seems reasonable enough of a PR, will size at a RiskMed instead of RiskLow to allow QA time to add tests if needed.