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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Cannot form the union of more than two tables","articleBody":"## Bug Report\r\n\r\n### Description\r\nI have a situation where I need to take the union over multiple tables (restriction or other methods will not work in this case). Taking the union over more than two tables throws an error.\r\n\r\n### Reproducibility\r\nInclude:\r\n- OS (MACOS)\r\n- Python Version 3.8.8\r\n- MySQL Deployment Strategy (remote)\r\n- DataJoint Version 0.13.2\r\n\r\nThis is a trivial example that seems to reproduce the issue:\r\n```python\r\n@schema\r\nclass Params(dj.Lookup):\r\n    definition = \"\"\"\r\n    params_id: tinyint unsigned\r\n    \"\"\"\r\n\r\nParams.insert([[x] for x in range(3)])\r\n\r\nparams = [Params \u0026 {'params_id': x} for x in range(3)]\r\n\r\nparams[0] + params[1] + params[2]\r\n```\r\n\r\nError stack:\r\n```console\r\n---------------------------------------------------------------------------\r\nTypeError                                 Traceback (most recent call last)\r\n~/anaconda3/envs/neural-data-kit/lib/python3.8/site-packages/IPython/core/formatters.py in __call__(self, obj)\r\n    700                 type_pprinters=self.type_printers,\r\n    701                 deferred_pprinters=self.deferred_printers)\r\n--\u003e 702             printer.pretty(obj)\r\n    703             printer.flush()\r\n    704             return stream.getvalue()\r\n\r\n~/anaconda3/envs/neural-data-kit/lib/python3.8/site-packages/IPython/lib/pretty.py in pretty(self, obj)\r\n    392                         if cls is not object \\\r\n    393                                 and callable(cls.__dict__.get('__repr__')):\r\n--\u003e 394                             return _repr_pprint(obj, self, cycle)\r\n    395 \r\n    396             return _default_pprint(obj, self, cycle)\r\n\r\n~/anaconda3/envs/neural-data-kit/lib/python3.8/site-packages/IPython/lib/pretty.py in _repr_pprint(obj, p, cycle)\r\n    698     \"\"\"A pprint that just redirects to the normal repr function.\"\"\"\r\n    699     # Find newlines and replace them with p.break_()\r\n--\u003e 700     output = repr(obj)\r\n    701     lines = output.splitlines()\r\n    702     with p.group():\r\n\r\n~/anaconda3/envs/neural-data-kit/lib/python3.8/site-packages/datajoint/expression.py in __repr__(self)\r\n    527         :rtype: str\r\n    528         \"\"\"\r\n--\u003e 529         return super().__repr__() if config['loglevel'].lower() == 'debug' else self.preview()\r\n    530 \r\n    531     def preview(self, limit=None, width=None):\r\n\r\n~/anaconda3/envs/neural-data-kit/lib/python3.8/site-packages/datajoint/expression.py in preview(self, limit, width)\r\n    531     def preview(self, limit=None, width=None):\r\n    532         \"\"\" :return: a string of preview of the contents of the query. \"\"\"\r\n--\u003e 533         return preview(self, limit, width)\r\n    534 \r\n    535     def _repr_html_(self):\r\n\r\n~/anaconda3/envs/neural-data-kit/lib/python3.8/site-packages/datajoint/preview.py in preview(query_expression, limit, width)\r\n     11     if width is None:\r\n     12         width = config['display.width']\r\n---\u003e 13     tuples = rel.fetch(limit=limit + 1, format=\"array\")\r\n     14     has_more = len(tuples) \u003e limit\r\n     15     tuples = tuples[:limit]\r\n\r\n~/anaconda3/envs/neural-data-kit/lib/python3.8/site-packages/datajoint/fetch.py in __call__(self, offset, limit, order_by, format, as_dict, squeeze, download_path, *attrs)\r\n    190                 ret = return_values[0] if len(attrs) == 1 else return_values\r\n    191         else:  # fetch all attributes as a numpy.record_array or pandas.DataFrame\r\n--\u003e 192             cur = self._expression.cursor(\r\n    193                 as_dict=as_dict, limit=limit, offset=offset, order_by=order_by)\r\n    194             heading = self._expression.heading\r\n\r\n~/anaconda3/envs/neural-data-kit/lib/python3.8/site-packages/datajoint/expression.py in cursor(self, offset, limit, order_by, as_dict)\r\n    511         if offset and limit is None:\r\n    512             raise DataJointError('limit is required when offset is set')\r\n--\u003e 513         sql = self.make_sql()\r\n    514         if order_by is not None:\r\n    515             sql += ' ORDER BY ' + ', '.join(order_by)\r\n\r\n~/anaconda3/envs/neural-data-kit/lib/python3.8/site-packages/datajoint/expression.py in make_sql(self, fields)\r\n    111             distinct=\"DISTINCT \" if distinct else \"\",\r\n    112             fields=self.heading.as_sql(fields or self.heading.names),\r\n--\u003e 113             from_=self.from_clause(), where=self.where_clause())\r\n    114 \r\n    115     # --------- query operators -----------\r\n\r\n~/anaconda3/envs/neural-data-kit/lib/python3.8/site-packages/datajoint/expression.py in from_clause(self)\r\n     91             self._subquery_alias_count) if isinstance(src, QueryExpression)\r\n     92             else src for src in self.support)\r\n---\u003e 93         clause = next(support)\r\n     94         for s, left in zip(support, self._left):\r\n     95             clause += ' NATURAL{left} JOIN {clause}'.format(\r\n\r\n~/anaconda3/envs/neural-data-kit/lib/python3.8/site-packages/datajoint/expression.py in (.0)\r\n     88 \r\n     89     def from_clause(self):\r\n---\u003e 90         support = ('(' + src.make_sql() + ') as `$%x`' % next(\r\n     91             self._subquery_alias_count) if isinstance(src, QueryExpression)\r\n     92             else src for src in self.support)\r\n\r\n~/anaconda3/envs/neural-data-kit/lib/python3.8/site-packages/datajoint/expression.py in make_sql(self)\r\n    627             fields = arg1.primary_key\r\n    628             return \"({sql1}) UNION ({sql2})\".format(\r\n--\u003e 629                 sql1=arg1.make_sql(fields),\r\n    630                 sql2=arg2.make_sql(fields))\r\n    631         # with secondary attributes, use union of left join with antijoin\r\n\r\nTypeError: make_sql() takes 1 positional argument but 2 were given\r\n```\r\n\r\n### Expected Behavior\r\nForming the union over two elements of `params` works as expected with the same setup as described above.\r\n\r\nNote: taking the union over more than two tables **does** work for python version 3.8.2 and datajoint version 0.12.6.\r\n","author":{"url":"https://github.com/najjajm","@type":"Person","name":"najjajm"},"datePublished":"2021-05-26T17:58:57.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/926/datajoint-python/issues/926"}