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        using_column_tables = _expand_using(scope, resolver)
 34        _qualify_columns(scope, resolver)
 35        if not isinstance(scope.expression, exp.UDTF):
 36            _expand_stars(scope, resolver, using_column_tables)
 37            _qualify_outputs(scope)
 38        _expand_alias_refs(scope, resolver)
 39        _expand_group_by(scope, resolver)
 40        _expand_order_by(scope)
 41
 42    return expression
 43
 44
 45def validate_qualify_columns(expression):
 46    """Raise an `OptimizeError` if any columns aren't qualified"""
 47    unqualified_columns = []
 48    for scope in traverse_scope(expression):
 49        if isinstance(scope.expression, exp.Select):
 50            unqualified_columns.extend(scope.unqualified_columns)
 51            if scope.external_columns and not scope.is_correlated_subquery:
 52                column = scope.external_columns[0]
 53                raise OptimizeError(f"Unknown table: '{column.table}' for column '{column}'")
 54
 55    if unqualified_columns:
 56        raise OptimizeError(f"Ambiguous columns: {unqualified_columns}")
 57    return expression
 58
 59
 60def _pop_table_column_aliases(derived_tables):
 61    """
 62    Remove table column aliases.
 63
 64    (e.g. SELECT ... FROM (SELECT ...) AS foo(col1, col2)
 65    """
 66    for derived_table in derived_tables:
 67        table_alias = derived_table.args.get("alias")
 68        if table_alias:
 69            table_alias.args.pop("columns", None)
 70
 71
 72def _expand_using(scope, resolver):
 73    joins = list(scope.find_all(exp.Join))
 74    names = {join.this.alias for join in joins}
 75    ordered = [key for key in scope.selected_sources if key not in names]
 76
 77    # Mapping of automatically joined column names to an ordered set of source names (dict).
 78    column_tables = {}
 79
 80    for join in joins:
 81        using = join.args.get("using")
 82
 83        if not using:
 84            continue
 85
 86        join_table = join.this.alias_or_name
 87
 88        columns = {}
 89
 90        for k in scope.selected_sources:
 91            if k in ordered:
 92                for column in resolver.get_source_columns(k):
 93                    if column not in columns:
 94                        columns[column] = k
 95
 96        ordered.append(join_table)
 97        join_columns = resolver.get_source_columns(join_table)
 98        conditions = []
 99
100        for identifier in using:
101            identifier = identifier.name
102            table = columns.get(identifier)
103
104            if not table or identifier not in join_columns:
105                raise OptimizeError(f"Cannot automatically join: {identifier}")
106
107            conditions.append(
108                exp.condition(
109                    exp.EQ(
110                        this=exp.column(identifier, table=table),
111                        expression=exp.column(identifier, table=join_table),
112                    )
113                )
114            )
115
116            # Set all values in the dict to None, because we only care about the key ordering
117            tables = column_tables.setdefault(identifier, {})
118            if table not in tables:
119                tables[table] = None
120            if join_table not in tables:
121                tables[join_table] = None
122
123        join.args.pop("using")
124        join.set("on", exp.and_(*conditions))
125
126    if column_tables:
127        for column in scope.columns:
128            if not column.table and column.name in column_tables:
129                tables = column_tables[column.name]
130                coalesce = [exp.column(column.name, table=table) for table in tables]
131                replacement = exp.Coalesce(this=coalesce[0], expressions=coalesce[1:])
132
133                # Ensure selects keep their output name
134                if isinstance(column.parent, exp.Select):
135                    replacement = exp.alias_(replacement, alias=column.name)
136
137                scope.replace(column, replacement)
138
139    return column_tables
140
141
142def _expand_alias_refs(scope, resolver):
143    selects = {}
144
145    # Replace references to select aliases
146    def transform(node, source_first=True):
147        if isinstance(node, exp.Column) and not node.table:
148            table = resolver.get_table(node.name)
149
150            # Source columns get priority over select aliases
151            if source_first and table:
152                node.set("table", table)
153                return node
154
155            if not selects:
156                for s in scope.selects:
157                    selects[s.alias_or_name] = s
158            select = selects.get(node.name)
159
160            if select:
161                scope.clear_cache()
162                if isinstance(select, exp.Alias):
163                    select = select.this
164                return select.copy()
165
166            node.set("table", table)
167        elif isinstance(node, exp.Expression) and not isinstance(node, exp.Subqueryable):
168            exp.replace_children(node, transform, source_first)
169
170        return node
171
172    for select in scope.expression.selects:
173        transform(select)
174
175    for modifier, source_first in (
176        ("where", True),
177        ("group", True),
178        ("having", False),
179    ):
180        transform(scope.expression.args.get(modifier), source_first=source_first)
181
182
183def _expand_group_by(scope, resolver):
184    group = scope.expression.args.get("group")
185    if not group:
186        return
187
188    group.set("expressions", _expand_positional_references(scope, group.expressions))
189    scope.expression.set("group", group)
190
191
192def _expand_order_by(scope):
193    order = scope.expression.args.get("order")
194    if not order:
195        return
196
197    ordereds = order.expressions
198    for ordered, new_expression in zip(
199        ordereds,
200        _expand_positional_references(scope, (o.this for o in ordereds)),
201    ):
202        ordered.set("this", new_expression)
203
204
205def _expand_positional_references(scope, expressions):
206    new_nodes = []
207    for node in expressions:
208        if node.is_int:
209            try:
210                select = scope.selects[int(node.name) - 1]
211            except IndexError:
212                raise OptimizeError(f"Unknown output column: {node.name}")
213            if isinstance(select, exp.Alias):
214                select = select.this
215            new_nodes.append(select.copy())
216            scope.clear_cache()
217        else:
218            new_nodes.append(node)
219
220    return new_nodes
221
222
223def _qualify_columns(scope, resolver):
224    """Disambiguate columns, ensuring each column specifies a source"""
225    for column in scope.columns:
226        column_table = column.table
227        column_name = column.name
228
229        if column_table and column_table in scope.sources:
230            source_columns = resolver.get_source_columns(column_table)
231            if source_columns and column_name not in source_columns and "*" not in source_columns:
232                raise OptimizeError(f"Unknown column: {column_name}")
233
234        if not column_table:
235            column_table = resolver.get_table(column_name)
236
237            # column_table can be a '' because bigquery unnest has no table alias
238            if column_table:
239                column.set("table", column_table)
240        elif column_table not in scope.sources:
241            # structs are used like tables (e.g. "struct"."field"), so they need to be qualified
242            # separately and represented as dot(dot(...(<table>.<column>, field1), field2, ...))
243
244            root, *parts = column.parts
245
246            if root.name in scope.sources:
247                # struct is already qualified, but we still need to change the AST representation
248                column_table = root
249                root, *parts = parts
250            else:
251                column_table = resolver.get_table(root.name)
252
253            if column_table:
254                column.replace(exp.Dot.build([exp.column(root, table=column_table), *parts]))
255
256    columns_missing_from_scope = []
257
258    # Determine whether each reference in the order by clause is to a column or an alias.
259    order = scope.expression.args.get("order")
260
261    if order:
262        for ordered in order.expressions:
263            for column in ordered.find_all(exp.Column):
264                if (
265                    not column.table
266                    and column.parent is not ordered
267                    and column.name in resolver.all_columns
268                ):
269                    columns_missing_from_scope.append(column)
270
271    # Determine whether each reference in the having clause is to a column or an alias.
272    having = scope.expression.args.get("having")
273
274    if having:
275        for column in having.find_all(exp.Column):
276            if (
277                not column.table
278                and column.find_ancestor(exp.AggFunc)
279                and column.name in resolver.all_columns
280            ):
281                columns_missing_from_scope.append(column)
282
283    for column in columns_missing_from_scope:
284        column_table = resolver.get_table(column.name)
285
286        if column_table:
287            column.set("table", column_table)
288
289
290def _expand_stars(scope, resolver, using_column_tables):
291    """Expand stars to lists of column selections"""
292
293    new_selections = []
294    except_columns = {}
295    replace_columns = {}
296    coalesced_columns = set()
297
298    for expression in scope.selects:
299        if isinstance(expression, exp.Star):
300            tables = list(scope.selected_sources)
301            _add_except_columns(expression, tables, except_columns)
302            _add_replace_columns(expression, tables, replace_columns)
303        elif expression.is_star:
304            tables = [expression.table]
305            _add_except_columns(expression.this, tables, except_columns)
306            _add_replace_columns(expression.this, tables, replace_columns)
307        else:
308            new_selections.append(expression)
309            continue
310
311        for table in tables:
312            if table not in scope.sources:
313                raise OptimizeError(f"Unknown table: {table}")
314            columns = resolver.get_source_columns(table, only_visible=True)
315
316            if columns and "*" not in columns:
317                table_id = id(table)
318                for name in columns:
319                    if name in using_column_tables and table in using_column_tables[name]:
320                        if name in coalesced_columns:
321                            continue
322
323                        coalesced_columns.add(name)
324                        tables = using_column_tables[name]
325                        coalesce = [exp.column(name, table=table) for table in tables]
326
327                        new_selections.append(
328                            exp.alias_(
329                                exp.Coalesce(this=coalesce[0], expressions=coalesce[1:]), alias=name
330                            )
331                        )
332                    elif name not in except_columns.get(table_id, set()):
333                        alias_ = replace_columns.get(table_id, {}).get(name, name)
334                        column = exp.column(name, table)
335                        new_selections.append(alias(column, alias_) if alias_ != name else column)
336            else:
337                return
338    scope.expression.set("expressions", new_selections)
339
340
341def _add_except_columns(expression, tables, except_columns):
342    except_ = expression.args.get("except")
343
344    if not except_:
345        return
346
347    columns = {e.name for e in except_}
348
349    for table in tables:
350        except_columns[id(table)] = columns
351
352
353def _add_replace_columns(expression, tables, replace_columns):
354    replace = expression.args.get("replace")
355
356    if not replace:
357        return
358
359    columns = {e.this.name: e.alias for e in replace}
360
361    for table in tables:
362        replace_columns[id(table)] = columns
363
364
365def _qualify_outputs(scope):
366    """Ensure all output columns are aliased"""
367    new_selections = []
368
369    for i, (selection, aliased_column) in enumerate(
370        itertools.zip_longest(scope.selects, scope.outer_column_list)
371    ):
372        if isinstance(selection, exp.Subquery):
373            if not selection.output_name:
374                selection.set("alias", exp.TableAlias(this=exp.to_identifier(f"_col_{i}")))
375        elif not isinstance(selection, exp.Alias) and not selection.is_star:
376            alias_ = alias(exp.column(""), alias=selection.output_name or f"_col_{i}")
377            alias_.set("this", selection)
378            selection = alias_
379
380        if aliased_column:
381            selection.set("alias", exp.to_identifier(aliased_column))
382
383        new_selections.append(selection)
384
385    scope.expression.set("expressions", new_selections)
386
387
388class Resolver:
389    """
390    Helper for resolving columns.
391
392    This is a class so we can lazily load some things and easily share them across functions.
393    """
394
395    def __init__(self, scope, schema):
396        self.scope = scope
397        self.schema = schema
398        self._source_columns = None
399        self._unambiguous_columns = None
400        self._all_columns = None
401
402    def get_table(self, column_name: str) -> t.Optional[exp.Identifier]:
403        """
404        Get the table for a column name.
405
406        Args:
407            column_name: The column name to find the table for.
408        Returns:
409            The table name if it can be found/inferred.
410        """
411        if self._unambiguous_columns is None:
412            self._unambiguous_columns = self._get_unambiguous_columns(
413                self._get_all_source_columns()
414            )
415
416        table_name = self._unambiguous_columns.get(column_name)
417
418        if not table_name:
419            sources_without_schema = tuple(
420                source
421                for source, columns in self._get_all_source_columns().items()
422                if not columns or "*" in columns
423            )
424            if len(sources_without_schema) == 1:
425                table_name = sources_without_schema[0]
426
427        if table_name not in self.scope.selected_sources:
428            return exp.to_identifier(table_name)
429
430        node, _ = self.scope.selected_sources.get(table_name)
431
432        if isinstance(node, exp.Subqueryable):
433            while node and node.alias != table_name:
434                node = node.parent
435
436        node_alias = node.args.get("alias")
437        if node_alias:
438            return node_alias.this
439
440        return exp.to_identifier(
441            table_name, quoted=node.this.quoted if isinstance(node, exp.Table) else None
442        )
443
444    @property
445    def all_columns(self):
446        """All available columns of all sources in this scope"""
447        if self._all_columns is None:
448            self._all_columns = {
449                column for columns in self._get_all_source_columns().values() for column in columns
450            }
451        return self._all_columns
452
453    def get_source_columns(self, name, only_visible=False):
454        """Resolve the source columns for a given source `name`"""
455        if name not in self.scope.sources:
456            raise OptimizeError(f"Unknown table: {name}")
457
458        source = self.scope.sources[name]
459
460        # If referencing a table, return the columns from the schema
461        if isinstance(source, exp.Table):
462            return self.schema.column_names(source, only_visible)
463
464        if isinstance(source, Scope) and isinstance(source.expression, exp.Values):
465            return source.expression.alias_column_names
466
467        # Otherwise, if referencing another scope, return that scope's named selects
468        return source.expression.named_selects
469
470    def _get_all_source_columns(self):
471        if self._source_columns is None:
472            self._source_columns = {
473                k: self.get_source_columns(k)
474                for k in itertools.chain(self.scope.selected_sources, self.scope.lateral_sources)
475            }
476        return self._source_columns
477
478    def _get_unambiguous_columns(self, source_columns):
479        """
480        Find all the unambiguous columns in sources.
481
482        Args:
483            source_columns (dict): Mapping of names to source columns
484        Returns:
485            dict: Mapping of column name to source name
486        """
487        if not source_columns:
488            return {}
489
490        source_columns = list(source_columns.items())
491
492        first_table, first_columns = source_columns[0]
493        unambiguous_columns = {col: first_table for col in self._find_unique_columns(first_columns)}
494        all_columns = set(unambiguous_columns)
495
496        for table, columns in source_columns[1:]:
497            unique = self._find_unique_columns(columns)
498            ambiguous = set(all_columns).intersection(unique)
499            all_columns.update(columns)
500            for column in ambiguous:
501                unambiguous_columns.pop(column, None)
502            for column in unique.difference(ambiguous):
503                unambiguous_columns[column] = table
504
505        return unambiguous_columns
506
507    @staticmethod
508    def _find_unique_columns(columns):
509        """
510        Find the unique columns in a list of columns.
511
512        Example:
513            >>> sorted(Resolver._find_unique_columns(["a", "b", "b", "c"]))
514            ['a', 'c']
515
516        This is necessary because duplicate column names are ambiguous.
517        """
518        counts = {}
519        for column in columns:
520            counts[column] = counts.get(column, 0) + 1
521        return {column for column, count in counts.items() if count == 1}