sqlglot.optimizer.qualify_columns

  1import itertools
  2import typing as t
  3
  4from sqlglot import alias, exp
  5from sqlglot.errors import OptimizeError
  6from sqlglot.optimizer.scope import Scope, traverse_scope
  7from sqlglot.schema import ensure_schema
  8
  9
 10def qualify_columns(expression, schema):
 11    """
 12    Rewrite sqlglot AST to have fully qualified columns.
 13
 14    Example:
 15        >>> import sqlglot
 16        >>> schema = {"tbl": {"col": "INT"}}
 17        >>> expression = sqlglot.parse_one("SELECT col FROM tbl")
 18        >>> qualify_columns(expression, schema).sql()
 19        'SELECT tbl.col AS col FROM tbl'
 20
 21    Args:
 22        expression (sqlglot.Expression): expression to qualify
 23        schema (dict|sqlglot.optimizer.Schema): Database schema
 24    Returns:
 25        sqlglot.Expression: qualified expression
 26    """
 27    schema = ensure_schema(schema)
 28
 29    for scope in traverse_scope(expression):
 30        resolver = Resolver(scope, schema)
 31        _pop_table_column_aliases(scope.ctes)
 32        _pop_table_column_aliases(scope.derived_tables)
 33        _expand_using(scope, resolver)
 34        _qualify_columns(scope, resolver)
 35        if not isinstance(scope.expression, exp.UDTF):
 36            _expand_stars(scope, resolver)
 37            _qualify_outputs(scope)
 38        _expand_group_by(scope, resolver)
 39        _expand_order_by(scope)
 40    return expression
 41
 42
 43def validate_qualify_columns(expression):
 44    """Raise an `OptimizeError` if any columns aren't qualified"""
 45    unqualified_columns = []
 46    for scope in traverse_scope(expression):
 47        if isinstance(scope.expression, exp.Select):
 48            unqualified_columns.extend(scope.unqualified_columns)
 49            if scope.external_columns and not scope.is_correlated_subquery:
 50                column = scope.external_columns[0]
 51                raise OptimizeError(f"Unknown table: '{column.table}' for column '{column}'")
 52
 53    if unqualified_columns:
 54        raise OptimizeError(f"Ambiguous columns: {unqualified_columns}")
 55    return expression
 56
 57
 58def _pop_table_column_aliases(derived_tables):
 59    """
 60    Remove table column aliases.
 61
 62    (e.g. SELECT ... FROM (SELECT ...) AS foo(col1, col2)
 63    """
 64    for derived_table in derived_tables:
 65        table_alias = derived_table.args.get("alias")
 66        if table_alias:
 67            table_alias.args.pop("columns", None)
 68
 69
 70def _expand_using(scope, resolver):
 71    joins = list(scope.expression.find_all(exp.Join))
 72    names = {join.this.alias for join in joins}
 73    ordered = [key for key in scope.selected_sources if key not in names]
 74
 75    # Mapping of automatically joined column names to source names
 76    column_tables = {}
 77
 78    for join in joins:
 79        using = join.args.get("using")
 80
 81        if not using:
 82            continue
 83
 84        join_table = join.this.alias_or_name
 85
 86        columns = {}
 87
 88        for k in scope.selected_sources:
 89            if k in ordered:
 90                for column in resolver.get_source_columns(k):
 91                    if column not in columns:
 92                        columns[column] = k
 93
 94        ordered.append(join_table)
 95        join_columns = resolver.get_source_columns(join_table)
 96        conditions = []
 97
 98        for identifier in using:
 99            identifier = identifier.name
100            table = columns.get(identifier)
101
102            if not table or identifier not in join_columns:
103                raise OptimizeError(f"Cannot automatically join: {identifier}")
104
105            conditions.append(
106                exp.condition(
107                    exp.EQ(
108                        this=exp.column(identifier, table=table),
109                        expression=exp.column(identifier, table=join_table),
110                    )
111                )
112            )
113
114            tables = column_tables.setdefault(identifier, [])
115            if table not in tables:
116                tables.append(table)
117            if join_table not in tables:
118                tables.append(join_table)
119
120        join.args.pop("using")
121        join.set("on", exp.and_(*conditions))
122
123    if column_tables:
124        for column in scope.columns:
125            if not column.table and column.name in column_tables:
126                tables = column_tables[column.name]
127                coalesce = [exp.column(column.name, table=table) for table in tables]
128                replacement = exp.Coalesce(this=coalesce[0], expressions=coalesce[1:])
129
130                # Ensure selects keep their output name
131                if isinstance(column.parent, exp.Select):
132                    replacement = exp.alias_(replacement, alias=column.name)
133
134                scope.replace(column, replacement)
135
136
137def _expand_group_by(scope, resolver):
138    group = scope.expression.args.get("group")
139    if not group:
140        return
141
142    # Replace references to select aliases
143    def transform(node, *_):
144        if isinstance(node, exp.Column) and not node.table:
145            table = resolver.get_table(node.name)
146
147            # Source columns get priority over select aliases
148            if table:
149                node.set("table", exp.to_identifier(table))
150                return node
151
152            selects = {s.alias_or_name: s for s in scope.selects}
153
154            select = selects.get(node.name)
155            if select:
156                scope.clear_cache()
157                if isinstance(select, exp.Alias):
158                    select = select.this
159                return select.copy()
160
161        return node
162
163    group.transform(transform, copy=False)
164    group.set("expressions", _expand_positional_references(scope, group.expressions))
165    scope.expression.set("group", group)
166
167
168def _expand_order_by(scope):
169    order = scope.expression.args.get("order")
170    if not order:
171        return
172
173    ordereds = order.expressions
174    for ordered, new_expression in zip(
175        ordereds,
176        _expand_positional_references(scope, (o.this for o in ordereds)),
177    ):
178        ordered.set("this", new_expression)
179
180
181def _expand_positional_references(scope, expressions):
182    new_nodes = []
183    for node in expressions:
184        if node.is_int:
185            try:
186                select = scope.selects[int(node.name) - 1]
187            except IndexError:
188                raise OptimizeError(f"Unknown output column: {node.name}")
189            if isinstance(select, exp.Alias):
190                select = select.this
191            new_nodes.append(select.copy())
192            scope.clear_cache()
193        else:
194            new_nodes.append(node)
195
196    return new_nodes
197
198
199def _qualify_columns(scope, resolver):
200    """Disambiguate columns, ensuring each column specifies a source"""
201    for column in scope.columns:
202        column_table = column.table
203        column_name = column.name
204
205        if column_table and column_table in scope.sources:
206            source_columns = resolver.get_source_columns(column_table)
207            if source_columns and column_name not in source_columns and "*" not in source_columns:
208                raise OptimizeError(f"Unknown column: {column_name}")
209
210        if not column_table:
211            column_table = resolver.get_table(column_name)
212
213            # column_table can be a '' because bigquery unnest has no table alias
214            if column_table:
215                column.set("table", exp.to_identifier(column_table))
216
217    columns_missing_from_scope = []
218    # Determine whether each reference in the order by clause is to a column or an alias.
219    for ordered in scope.find_all(exp.Ordered):
220        for column in ordered.find_all(exp.Column):
221            if (
222                not column.table
223                and column.parent is not ordered
224                and column.name in resolver.all_columns
225            ):
226                columns_missing_from_scope.append(column)
227
228    # Determine whether each reference in the having clause is to a column or an alias.
229    for having in scope.find_all(exp.Having):
230        for column in having.find_all(exp.Column):
231            if (
232                not column.table
233                and column.find_ancestor(exp.AggFunc)
234                and column.name in resolver.all_columns
235            ):
236                columns_missing_from_scope.append(column)
237
238    for column in columns_missing_from_scope:
239        column_table = resolver.get_table(column.name)
240
241        if column_table:
242            column.set("table", exp.to_identifier(column_table))
243
244
245def _expand_stars(scope, resolver):
246    """Expand stars to lists of column selections"""
247
248    new_selections = []
249    except_columns = {}
250    replace_columns = {}
251
252    for expression in scope.selects:
253        if isinstance(expression, exp.Star):
254            tables = list(scope.selected_sources)
255            _add_except_columns(expression, tables, except_columns)
256            _add_replace_columns(expression, tables, replace_columns)
257        elif expression.is_star:
258            tables = [expression.table]
259            _add_except_columns(expression.this, tables, except_columns)
260            _add_replace_columns(expression.this, tables, replace_columns)
261        else:
262            new_selections.append(expression)
263            continue
264
265        for table in tables:
266            if table not in scope.sources:
267                raise OptimizeError(f"Unknown table: {table}")
268            columns = resolver.get_source_columns(table, only_visible=True)
269
270            if columns and "*" not in columns:
271                table_id = id(table)
272                for name in columns:
273                    if name not in except_columns.get(table_id, set()):
274                        alias_ = replace_columns.get(table_id, {}).get(name, name)
275                        column = exp.column(name, table)
276                        new_selections.append(alias(column, alias_) if alias_ != name else column)
277            else:
278                return
279    scope.expression.set("expressions", new_selections)
280
281
282def _add_except_columns(expression, tables, except_columns):
283    except_ = expression.args.get("except")
284
285    if not except_:
286        return
287
288    columns = {e.name for e in except_}
289
290    for table in tables:
291        except_columns[id(table)] = columns
292
293
294def _add_replace_columns(expression, tables, replace_columns):
295    replace = expression.args.get("replace")
296
297    if not replace:
298        return
299
300    columns = {e.this.name: e.alias for e in replace}
301
302    for table in tables:
303        replace_columns[id(table)] = columns
304
305
306def _qualify_outputs(scope):
307    """Ensure all output columns are aliased"""
308    new_selections = []
309
310    for i, (selection, aliased_column) in enumerate(
311        itertools.zip_longest(scope.selects, scope.outer_column_list)
312    ):
313        if isinstance(selection, exp.Subquery):
314            if not selection.output_name:
315                selection.set("alias", exp.TableAlias(this=exp.to_identifier(f"_col_{i}")))
316        elif not isinstance(selection, exp.Alias) and not selection.is_star:
317            alias_ = alias(exp.column(""), alias=selection.output_name or f"_col_{i}")
318            alias_.set("this", selection)
319            selection = alias_
320
321        if aliased_column:
322            selection.set("alias", exp.to_identifier(aliased_column))
323
324        new_selections.append(selection)
325
326    scope.expression.set("expressions", new_selections)
327
328
329class Resolver:
330    """
331    Helper for resolving columns.
332
333    This is a class so we can lazily load some things and easily share them across functions.
334    """
335
336    def __init__(self, scope, schema):
337        self.scope = scope
338        self.schema = schema
339        self._source_columns = None
340        self._unambiguous_columns = None
341        self._all_columns = None
342
343    def get_table(self, column_name: str) -> t.Optional[str]:
344        """
345        Get the table for a column name.
346
347        Args:
348            column_name: The column name to find the table for.
349        Returns:
350            The table name if it can be found/inferred.
351        """
352        if self._unambiguous_columns is None:
353            self._unambiguous_columns = self._get_unambiguous_columns(
354                self._get_all_source_columns()
355            )
356
357        table = self._unambiguous_columns.get(column_name)
358
359        if not table:
360            sources_without_schema = tuple(
361                source
362                for source, columns in self._get_all_source_columns().items()
363                if not columns or "*" in columns
364            )
365            if len(sources_without_schema) == 1:
366                return sources_without_schema[0]
367
368        return table
369
370    @property
371    def all_columns(self):
372        """All available columns of all sources in this scope"""
373        if self._all_columns is None:
374            self._all_columns = {
375                column for columns in self._get_all_source_columns().values() for column in columns
376            }
377        return self._all_columns
378
379    def get_source_columns(self, name, only_visible=False):
380        """Resolve the source columns for a given source `name`"""
381        if name not in self.scope.sources:
382            raise OptimizeError(f"Unknown table: {name}")
383
384        source = self.scope.sources[name]
385
386        # If referencing a table, return the columns from the schema
387        if isinstance(source, exp.Table):
388            return self.schema.column_names(source, only_visible)
389
390        if isinstance(source, Scope) and isinstance(source.expression, exp.Values):
391            return source.expression.alias_column_names
392
393        # Otherwise, if referencing another scope, return that scope's named selects
394        return source.expression.named_selects
395
396    def _get_all_source_columns(self):
397        if self._source_columns is None:
398            self._source_columns = {
399                k: self.get_source_columns(k)
400                for k in itertools.chain(self.scope.selected_sources, self.scope.lateral_sources)
401            }
402        return self._source_columns
403
404    def _get_unambiguous_columns(self, source_columns):
405        """
406        Find all the unambiguous columns in sources.
407
408        Args:
409            source_columns (dict): Mapping of names to source columns
410        Returns:
411            dict: Mapping of column name to source name
412        """
413        if not source_columns:
414            return {}
415
416        source_columns = list(source_columns.items())
417
418        first_table, first_columns = source_columns[0]
419        unambiguous_columns = {col: first_table for col in self._find_unique_columns(first_columns)}
420        all_columns = set(unambiguous_columns)
421
422        for table, columns in source_columns[1:]:
423            unique = self._find_unique_columns(columns)
424            ambiguous = set(all_columns).intersection(unique)
425            all_columns.update(columns)
426            for column in ambiguous:
427                unambiguous_columns.pop(column, None)
428            for column in unique.difference(ambiguous):
429                unambiguous_columns[column] = table
430
431        return unambiguous_columns
432
433    @staticmethod
434    def _find_unique_columns(columns):
435        """
436        Find the unique columns in a list of columns.
437
438        Example:
439            >>> sorted(Resolver._find_unique_columns(["a", "b", "b", "c"]))
440            ['a', 'c']
441
442        This is necessary because duplicate column names are ambiguous.
443        """
444        counts = {}
445        for column in columns:
446            counts[column] = counts.get(column, 0) + 1
447        return {column for column, count in counts.items() if count == 1}