AttributeError: 'DropTable' object has no attribute 'if_exists' about clickhouse-sqlalchemy

[xzkostyan]

Hi, @wuhuanyan

if_exists was designed as extension of table.drop syntax.

When SA reflect table from database (see query in clickhouse log DESCRIBE TABLE test_drop FORMAT TabSeparatedWithNamesAndTypes) it constructs instance of default Table class. That's why drop.if_exists in visit_drop_table doesn't work.

If we comment or change this string to something like this: if getattr(drop, 'if_exists', False). We will get following error:

~/clickhouse-sqlalchemy/clickhouse_sqlalchemy/drivers/base.py in post_create_table(self, table)
    286 
    287         if not engine:
--> 288             raise exc.CompileError("No engine for table '%s'" % table.name)
    289 
    290         return ' ENGINE = ' + self.process(engine)

CompileError: No engine for table 'test_drop'

Engine is required parameter for table creation. I think it also should be reflected from database via parsing SHOW CREATE TABLE testing query.

In current pandas to_sql interface it seems impossible to pass additional parameters such as CH Engine.

I'd recommend you not to drop/create table as temporary solution. Or you can drop/create tables via sqlalchemy. See README for examples.

[wuhuanyan]

I changed it like this
clickhouse_sqlalchemy/drivers/base.py
294th lines

    def visit_drop_table(self, drop):
        text = '\nDROP TABLE IF EXISTS '
        # if drop.if_exists:
        #     text += 'IF EXISTS '
        return text + self.preparer.format_table(drop.element)

[wuhuanyan]

In addition to other questions
How do you pass ENGINE parameters of CREATE TABLE through pandas.dataframe.to_sql?

[xzkostyan]

Fixed in #94.