mssql_drop_foreign_key generates statement that raises pyodbc.ProgrammingError (Incorrect syntax near '`')

[Nuqlear]

Describe the bug

op.drop_column("assignment", "employee_profile_id", mssql_drop_foreign_key=True)

This line is generating the following statement:

declare @const_name varchar(256)
select @const_name = [name] from
sys.foreign_keys fk join sys.foreign_key_columns fkc
on fk.object_id=fkc.constraint_object_id
where fkc.parent_object_id = object_id('assignment')
`and col_name(fkc.parent_object_id, fkc.parent_column_id) = 'employee_profile_id'
exec('alter table assignment drop constraint ' + @const_name)

which leads to pyodbc.ProgrammingError:

pyodbc.ProgrammingError: ('42000', "[42000] [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Incorrect syntax near '`'. (102) (SQLExecDirectW)")

Expected behavior
Foreign key dropped alongside column without errors.

Versions.

• OS: Ubuntu 18.04
• Python: 3.7.4
• Alembic: 1.4.2
• SQLAlchemy: 1.3.14
• Database: Azure SQL Server
• DBAPI: pyodbc==4.0.30

[CaselIT]

Strange. Seems to be a typo introduced in 6e30795.

[CaselIT]

@gordthompson I'm not familiar sql server, do backticks (`) have a particular meaning in it?

[sqla-tester]

Oleg Shigorin has proposed a fix for this issue in the master branch:

Fixes #716. Remove typo in _exec_drop_col_fk_constraint https://gerrit.sqlalchemy.org/c/sqlalchemy/alembic/+/2105

[gordthompson]

@gordthompson I'm not familiar sql server, do backticks (`) have a particular meaning in it?

AFAIK, no.

[CaselIT]

thanks, should be a typo then.

[zzzeek]

how did this ever work? user at #621 (comment) maybe didnt actually run this part?

[sqla-tester]

Oleg Shigorin has proposed a fix for this issue in the master branch:

Remove typo in _exec_drop_col_fk_constraint https://gerrit.sqlalchemy.org/c/sqlalchemy/alembic/+/2105