Ensure the default is declared in the same statement for new columns

[duncan3dc]

Q	A
Type	bug
BC Break	no
Fixed issues	#2265

Summary

When adding columns to tables that already contain data, SQL Server requires that the default constraint is declared in the same statement, Doctrine currently generates a separate ADD CONSTRAINT statement, which means the add column statement errors with something like:

SQLSTATE [42000, 4901]: [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]
ALTER TABLE only allows columns to be added that can contain nulls, or have a DEFAULT
definition specified, or the column being added is an identity or timestamp column,
or alternatively if none of the previous conditions are satisfied the table must be
empty to allow addition of this column. Column 'addcolumn' cannot be added
to non-empty table 'mytable' because it does not satisfy these conditions.

[morozov]

Thank you for the patch, @duncan3dc. In addition to the unit test, it would be good to have an integration test that confirms that the fixed SQL also works and produces the expected results. See the testing guidelines for more details.

[duncan3dc]

Of course, I've had a go at that in 2ea06d1 it fails against the 2.12.x branch and passes with this PR

[morozov]

Looks good. Please squash into one commit since the code change and both tests belong together.

[morozov]

This is out of the scope of this issue but it looks like this code incorrectly handles the DEFAULT NULL case.

[morozov]

Thanks, @duncan3dc!