sqlglot.optimizer.scope

  1from __future__ import annotations
  2
  3import itertools
  4import logging
  5import typing as t
  6from collections import defaultdict
  7from enum import Enum, auto
  8
  9from sqlglot import exp
 10from sqlglot.errors import OptimizeError
 11from sqlglot.helper import ensure_collection, find_new_name, seq_get
 12
 13logger = logging.getLogger("sqlglot")
 14
 15TRAVERSABLES = (exp.Query, exp.DDL, exp.DML)
 16
 17
 18class ScopeType(Enum):
 19    ROOT = auto()
 20    SUBQUERY = auto()
 21    DERIVED_TABLE = auto()
 22    CTE = auto()
 23    UNION = auto()
 24    UDTF = auto()
 25
 26
 27class Scope:
 28    """
 29    Selection scope.
 30
 31    Attributes:
 32        expression (exp.Select|exp.SetOperation): Root expression of this scope
 33        sources (dict[str, exp.Table|Scope]): Mapping of source name to either
 34            a Table expression or another Scope instance. For example:
 35                SELECT * FROM x                     {"x": Table(this="x")}
 36                SELECT * FROM x AS y                {"y": Table(this="x")}
 37                SELECT * FROM (SELECT ...) AS y     {"y": Scope(...)}
 38        lateral_sources (dict[str, exp.Table|Scope]): Sources from laterals
 39            For example:
 40                SELECT c FROM x LATERAL VIEW EXPLODE (a) AS c;
 41            The LATERAL VIEW EXPLODE gets x as a source.
 42        cte_sources (dict[str, Scope]): Sources from CTES
 43        outer_columns (list[str]): If this is a derived table or CTE, and the outer query
 44            defines a column list for the alias of this scope, this is that list of columns.
 45            For example:
 46                SELECT * FROM (SELECT ...) AS y(col1, col2)
 47            The inner query would have `["col1", "col2"]` for its `outer_columns`
 48        parent (Scope): Parent scope
 49        scope_type (ScopeType): Type of this scope, relative to it's parent
 50        subquery_scopes (list[Scope]): List of all child scopes for subqueries
 51        cte_scopes (list[Scope]): List of all child scopes for CTEs
 52        derived_table_scopes (list[Scope]): List of all child scopes for derived_tables
 53        udtf_scopes (list[Scope]): List of all child scopes for user defined tabular functions
 54        table_scopes (list[Scope]): derived_table_scopes + udtf_scopes, in the order that they're defined
 55        union_scopes (list[Scope, Scope]): If this Scope is for a Union expression, this will be
 56            a list of the left and right child scopes.
 57    """
 58
 59    def __init__(
 60        self,
 61        expression,
 62        sources=None,
 63        outer_columns=None,
 64        parent=None,
 65        scope_type=ScopeType.ROOT,
 66        lateral_sources=None,
 67        cte_sources=None,
 68        can_be_correlated=None,
 69    ):
 70        self.expression = expression
 71        self.sources = sources or {}
 72        self.lateral_sources = lateral_sources or {}
 73        self.cte_sources = cte_sources or {}
 74        self.sources.update(self.lateral_sources)
 75        self.sources.update(self.cte_sources)
 76        self.outer_columns = outer_columns or []
 77        self.parent = parent
 78        self.scope_type = scope_type
 79        self.subquery_scopes = []
 80        self.derived_table_scopes = []
 81        self.table_scopes = []
 82        self.cte_scopes = []
 83        self.union_scopes = []
 84        self.udtf_scopes = []
 85        self.can_be_correlated = can_be_correlated
 86        self.clear_cache()
 87
 88    def clear_cache(self):
 89        self._collected = False
 90        self._raw_columns = None
 91        self._table_columns = None
 92        self._stars = None
 93        self._derived_tables = None
 94        self._udtfs = None
 95        self._tables = None
 96        self._ctes = None
 97        self._subqueries = None
 98        self._selected_sources = None
 99        self._columns = None
100        self._external_columns = None
101        self._join_hints = None
102        self._pivots = None
103        self._references = None
104        self._semi_anti_join_tables = None
105
106    def branch(
107        self, expression, scope_type, sources=None, cte_sources=None, lateral_sources=None, **kwargs
108    ):
109        """Branch from the current scope to a new, inner scope"""
110        return Scope(
111            expression=expression.unnest(),
112            sources=sources.copy() if sources else None,
113            parent=self,
114            scope_type=scope_type,
115            cte_sources={**self.cte_sources, **(cte_sources or {})},
116            lateral_sources=lateral_sources.copy() if lateral_sources else None,
117            can_be_correlated=self.can_be_correlated
118            or scope_type in (ScopeType.SUBQUERY, ScopeType.UDTF),
119            **kwargs,
120        )
121
122    def _collect(self):
123        self._tables = []
124        self._ctes = []
125        self._subqueries = []
126        self._derived_tables = []
127        self._udtfs = []
128        self._raw_columns = []
129        self._table_columns = []
130        self._stars = []
131        self._join_hints = []
132        self._semi_anti_join_tables = set()
133
134        for node in self.walk(bfs=False):
135            if node is self.expression:
136                continue
137
138            if isinstance(node, exp.Dot) and node.is_star:
139                self._stars.append(node)
140            elif isinstance(node, exp.Column):
141                if isinstance(node.this, exp.Star):
142                    self._stars.append(node)
143                else:
144                    self._raw_columns.append(node)
145            elif isinstance(node, exp.Table) and not isinstance(node.parent, exp.JoinHint):
146                parent = node.parent
147                if isinstance(parent, exp.Join) and parent.is_semi_or_anti_join:
148                    self._semi_anti_join_tables.add(node.alias_or_name)
149
150                self._tables.append(node)
151            elif isinstance(node, exp.JoinHint):
152                self._join_hints.append(node)
153            elif isinstance(node, exp.UDTF):
154                self._udtfs.append(node)
155            elif isinstance(node, exp.CTE):
156                self._ctes.append(node)
157            elif _is_derived_table(node) and _is_from_or_join(node):
158                self._derived_tables.append(node)
159            elif isinstance(node, exp.UNWRAPPED_QUERIES):
160                self._subqueries.append(node)
161            elif isinstance(node, exp.TableColumn):
162                self._table_columns.append(node)
163
164        self._collected = True
165
166    def _ensure_collected(self):
167        if not self._collected:
168            self._collect()
169
170    def walk(self, bfs=True, prune=None):
171        return walk_in_scope(self.expression, bfs=bfs, prune=None)
172
173    def find(self, *expression_types, bfs=True):
174        return find_in_scope(self.expression, expression_types, bfs=bfs)
175
176    def find_all(self, *expression_types, bfs=True):
177        return find_all_in_scope(self.expression, expression_types, bfs=bfs)
178
179    def replace(self, old, new):
180        """
181        Replace `old` with `new`.
182
183        This can be used instead of `exp.Expression.replace` to ensure the `Scope` is kept up-to-date.
184
185        Args:
186            old (exp.Expression): old node
187            new (exp.Expression): new node
188        """
189        old.replace(new)
190        self.clear_cache()
191
192    @property
193    def tables(self):
194        """
195        List of tables in this scope.
196
197        Returns:
198            list[exp.Table]: tables
199        """
200        self._ensure_collected()
201        return self._tables
202
203    @property
204    def ctes(self):
205        """
206        List of CTEs in this scope.
207
208        Returns:
209            list[exp.CTE]: ctes
210        """
211        self._ensure_collected()
212        return self._ctes
213
214    @property
215    def derived_tables(self):
216        """
217        List of derived tables in this scope.
218
219        For example:
220            SELECT * FROM (SELECT ...) <- that's a derived table
221
222        Returns:
223            list[exp.Subquery]: derived tables
224        """
225        self._ensure_collected()
226        return self._derived_tables
227
228    @property
229    def udtfs(self):
230        """
231        List of "User Defined Tabular Functions" in this scope.
232
233        Returns:
234            list[exp.UDTF]: UDTFs
235        """
236        self._ensure_collected()
237        return self._udtfs
238
239    @property
240    def subqueries(self):
241        """
242        List of subqueries in this scope.
243
244        For example:
245            SELECT * FROM x WHERE a IN (SELECT ...) <- that's a subquery
246
247        Returns:
248            list[exp.Select | exp.SetOperation]: subqueries
249        """
250        self._ensure_collected()
251        return self._subqueries
252
253    @property
254    def stars(self) -> t.List[exp.Column | exp.Dot]:
255        """
256        List of star expressions (columns or dots) in this scope.
257        """
258        self._ensure_collected()
259        return self._stars
260
261    @property
262    def columns(self):
263        """
264        List of columns in this scope.
265
266        Returns:
267            list[exp.Column]: Column instances in this scope, plus any
268                Columns that reference this scope from correlated subqueries.
269        """
270        if self._columns is None:
271            self._ensure_collected()
272            columns = self._raw_columns
273
274            external_columns = [
275                column
276                for scope in itertools.chain(
277                    self.subquery_scopes,
278                    self.udtf_scopes,
279                    (dts for dts in self.derived_table_scopes if dts.can_be_correlated),
280                )
281                for column in scope.external_columns
282            ]
283
284            named_selects = set(self.expression.named_selects)
285
286            self._columns = []
287            for column in columns + external_columns:
288                ancestor = column.find_ancestor(
289                    exp.Select,
290                    exp.Qualify,
291                    exp.Order,
292                    exp.Having,
293                    exp.Hint,
294                    exp.Table,
295                    exp.Star,
296                    exp.Distinct,
297                )
298                if (
299                    not ancestor
300                    or column.table
301                    or isinstance(ancestor, exp.Select)
302                    or (isinstance(ancestor, exp.Table) and not isinstance(ancestor.this, exp.Func))
303                    or (
304                        isinstance(ancestor, (exp.Order, exp.Distinct))
305                        and (
306                            isinstance(ancestor.parent, (exp.Window, exp.WithinGroup))
307                            or not isinstance(ancestor.parent, exp.Select)
308                            or column.name not in named_selects
309                        )
310                    )
311                    or (isinstance(ancestor, exp.Star) and not column.arg_key == "except")
312                ):
313                    self._columns.append(column)
314
315        return self._columns
316
317    @property
318    def table_columns(self):
319        if self._table_columns is None:
320            self._ensure_collected()
321
322        return self._table_columns
323
324    @property
325    def selected_sources(self):
326        """
327        Mapping of nodes and sources that are actually selected from in this scope.
328
329        That is, all tables in a schema are selectable at any point. But a
330        table only becomes a selected source if it's included in a FROM or JOIN clause.
331
332        Returns:
333            dict[str, (exp.Table|exp.Select, exp.Table|Scope)]: selected sources and nodes
334        """
335        if self._selected_sources is None:
336            result = {}
337
338            for name, node in self.references:
339                if name in self._semi_anti_join_tables:
340                    # The RHS table of SEMI/ANTI joins shouldn't be collected as a
341                    # selected source
342                    continue
343
344                if name in result:
345                    raise OptimizeError(f"Alias already used: {name}")
346                if name in self.sources:
347                    result[name] = (node, self.sources[name])
348
349            self._selected_sources = result
350        return self._selected_sources
351
352    @property
353    def references(self) -> t.List[t.Tuple[str, exp.Expression]]:
354        if self._references is None:
355            self._references = []
356
357            for table in self.tables:
358                self._references.append((table.alias_or_name, table))
359            for expression in itertools.chain(self.derived_tables, self.udtfs):
360                self._references.append(
361                    (
362                        _get_source_alias(expression),
363                        expression if expression.args.get("pivots") else expression.unnest(),
364                    )
365                )
366
367        return self._references
368
369    @property
370    def external_columns(self):
371        """
372        Columns that appear to reference sources in outer scopes.
373
374        Returns:
375            list[exp.Column]: Column instances that don't reference
376                sources in the current scope.
377        """
378        if self._external_columns is None:
379            if isinstance(self.expression, exp.SetOperation):
380                left, right = self.union_scopes
381                self._external_columns = left.external_columns + right.external_columns
382            else:
383                self._external_columns = [
384                    c
385                    for c in self.columns
386                    if c.table not in self.selected_sources
387                    and c.table not in self.semi_or_anti_join_tables
388                ]
389
390        return self._external_columns
391
392    @property
393    def unqualified_columns(self):
394        """
395        Unqualified columns in the current scope.
396
397        Returns:
398             list[exp.Column]: Unqualified columns
399        """
400        return [c for c in self.columns if not c.table]
401
402    @property
403    def join_hints(self):
404        """
405        Hints that exist in the scope that reference tables
406
407        Returns:
408            list[exp.JoinHint]: Join hints that are referenced within the scope
409        """
410        if self._join_hints is None:
411            return []
412        return self._join_hints
413
414    @property
415    def pivots(self):
416        if not self._pivots:
417            self._pivots = [
418                pivot for _, node in self.references for pivot in node.args.get("pivots") or []
419            ]
420
421        return self._pivots
422
423    @property
424    def semi_or_anti_join_tables(self):
425        return self._semi_anti_join_tables or set()
426
427    def source_columns(self, source_name):
428        """
429        Get all columns in the current scope for a particular source.
430
431        Args:
432            source_name (str): Name of the source
433        Returns:
434            list[exp.Column]: Column instances that reference `source_name`
435        """
436        return [column for column in self.columns if column.table == source_name]
437
438    @property
439    def is_subquery(self):
440        """Determine if this scope is a subquery"""
441        return self.scope_type == ScopeType.SUBQUERY
442
443    @property
444    def is_derived_table(self):
445        """Determine if this scope is a derived table"""
446        return self.scope_type == ScopeType.DERIVED_TABLE
447
448    @property
449    def is_union(self):
450        """Determine if this scope is a union"""
451        return self.scope_type == ScopeType.UNION
452
453    @property
454    def is_cte(self):
455        """Determine if this scope is a common table expression"""
456        return self.scope_type == ScopeType.CTE
457
458    @property
459    def is_root(self):
460        """Determine if this is the root scope"""
461        return self.scope_type == ScopeType.ROOT
462
463    @property
464    def is_udtf(self):
465        """Determine if this scope is a UDTF (User Defined Table Function)"""
466        return self.scope_type == ScopeType.UDTF
467
468    @property
469    def is_correlated_subquery(self):
470        """Determine if this scope is a correlated subquery"""
471        return bool(self.can_be_correlated and self.external_columns)
472
473    def rename_source(self, old_name, new_name):
474        """Rename a source in this scope"""
475        columns = self.sources.pop(old_name or "", [])
476        self.sources[new_name] = columns
477
478    def add_source(self, name, source):
479        """Add a source to this scope"""
480        self.sources[name] = source
481        self.clear_cache()
482
483    def remove_source(self, name):
484        """Remove a source from this scope"""
485        self.sources.pop(name, None)
486        self.clear_cache()
487
488    def __repr__(self):
489        return f"Scope<{self.expression.sql()}>"
490
491    def traverse(self):
492        """
493        Traverse the scope tree from this node.
494
495        Yields:
496            Scope: scope instances in depth-first-search post-order
497        """
498        stack = [self]
499        result = []
500        while stack:
501            scope = stack.pop()
502            result.append(scope)
503            stack.extend(
504                itertools.chain(
505                    scope.cte_scopes,
506                    scope.union_scopes,
507                    scope.table_scopes,
508                    scope.subquery_scopes,
509                )
510            )
511
512        yield from reversed(result)
513
514    def ref_count(self):
515        """
516        Count the number of times each scope in this tree is referenced.
517
518        Returns:
519            dict[int, int]: Mapping of Scope instance ID to reference count
520        """
521        scope_ref_count = defaultdict(lambda: 0)
522
523        for scope in self.traverse():
524            for _, source in scope.selected_sources.values():
525                scope_ref_count[id(source)] += 1
526
527            for name in scope._semi_anti_join_tables:
528                # semi/anti join sources are not actually selected but we still need to
529                # increment their ref count to avoid them being optimized away
530                if name in scope.sources:
531                    scope_ref_count[id(scope.sources[name])] += 1
532
533        return scope_ref_count
534
535
536def traverse_scope(expression: exp.Expression) -> t.List[Scope]:
537    """
538    Traverse an expression by its "scopes".
539
540    "Scope" represents the current context of a Select statement.
541
542    This is helpful for optimizing queries, where we need more information than
543    the expression tree itself. For example, we might care about the source
544    names within a subquery. Returns a list because a generator could result in
545    incomplete properties which is confusing.
546
547    Examples:
548        >>> import sqlglot
549        >>> expression = sqlglot.parse_one("SELECT a FROM (SELECT a FROM x) AS y")
550        >>> scopes = traverse_scope(expression)
551        >>> scopes[0].expression.sql(), list(scopes[0].sources)
552        ('SELECT a FROM x', ['x'])
553        >>> scopes[1].expression.sql(), list(scopes[1].sources)
554        ('SELECT a FROM (SELECT a FROM x) AS y', ['y'])
555
556    Args:
557        expression: Expression to traverse
558
559    Returns:
560        A list of the created scope instances
561    """
562    if isinstance(expression, TRAVERSABLES):
563        return list(_traverse_scope(Scope(expression)))
564    return []
565
566
567def build_scope(expression: exp.Expression) -> t.Optional[Scope]:
568    """
569    Build a scope tree.
570
571    Args:
572        expression: Expression to build the scope tree for.
573
574    Returns:
575        The root scope
576    """
577    return seq_get(traverse_scope(expression), -1)
578
579
580def _traverse_scope(scope):
581    expression = scope.expression
582
583    if isinstance(expression, exp.Select):
584        yield from _traverse_select(scope)
585    elif isinstance(expression, exp.SetOperation):
586        yield from _traverse_ctes(scope)
587        yield from _traverse_union(scope)
588        return
589    elif isinstance(expression, exp.Subquery):
590        if scope.is_root:
591            yield from _traverse_select(scope)
592        else:
593            yield from _traverse_subqueries(scope)
594    elif isinstance(expression, exp.Table):
595        yield from _traverse_tables(scope)
596    elif isinstance(expression, exp.UDTF):
597        yield from _traverse_udtfs(scope)
598    elif isinstance(expression, exp.DDL):
599        if isinstance(expression.expression, exp.Query):
600            yield from _traverse_ctes(scope)
601            yield from _traverse_scope(Scope(expression.expression, cte_sources=scope.cte_sources))
602        return
603    elif isinstance(expression, exp.DML):
604        yield from _traverse_ctes(scope)
605        for query in find_all_in_scope(expression, exp.Query):
606            # This check ensures we don't yield the CTE/nested queries twice
607            if not isinstance(query.parent, (exp.CTE, exp.Subquery)):
608                yield from _traverse_scope(Scope(query, cte_sources=scope.cte_sources))
609        return
610    else:
611        logger.warning("Cannot traverse scope %s with type '%s'", expression, type(expression))
612        return
613
614    yield scope
615
616
617def _traverse_select(scope):
618    yield from _traverse_ctes(scope)
619    yield from _traverse_tables(scope)
620    yield from _traverse_subqueries(scope)
621
622
623def _traverse_union(scope):
624    prev_scope = None
625    union_scope_stack = [scope]
626    expression_stack = [scope.expression.right, scope.expression.left]
627
628    while expression_stack:
629        expression = expression_stack.pop()
630        union_scope = union_scope_stack[-1]
631
632        new_scope = union_scope.branch(
633            expression,
634            outer_columns=union_scope.outer_columns,
635            scope_type=ScopeType.UNION,
636        )
637
638        if isinstance(expression, exp.SetOperation):
639            yield from _traverse_ctes(new_scope)
640
641            union_scope_stack.append(new_scope)
642            expression_stack.extend([expression.right, expression.left])
643            continue
644
645        for scope in _traverse_scope(new_scope):
646            yield scope
647
648        if prev_scope:
649            union_scope_stack.pop()
650            union_scope.union_scopes = [prev_scope, scope]
651            prev_scope = union_scope
652
653            yield union_scope
654        else:
655            prev_scope = scope
656
657
658def _traverse_ctes(scope):
659    sources = {}
660
661    for cte in scope.ctes:
662        cte_name = cte.alias
663
664        # if the scope is a recursive cte, it must be in the form of base_case UNION recursive.
665        # thus the recursive scope is the first section of the union.
666        with_ = scope.expression.args.get("with")
667        if with_ and with_.recursive:
668            union = cte.this
669
670            if isinstance(union, exp.SetOperation):
671                sources[cte_name] = scope.branch(union.this, scope_type=ScopeType.CTE)
672
673        child_scope = None
674
675        for child_scope in _traverse_scope(
676            scope.branch(
677                cte.this,
678                cte_sources=sources,
679                outer_columns=cte.alias_column_names,
680                scope_type=ScopeType.CTE,
681            )
682        ):
683            yield child_scope
684
685        # append the final child_scope yielded
686        if child_scope:
687            sources[cte_name] = child_scope
688            scope.cte_scopes.append(child_scope)
689
690    scope.sources.update(sources)
691    scope.cte_sources.update(sources)
692
693
694def _is_derived_table(expression: exp.Subquery) -> bool:
695    """
696    We represent (tbl1 JOIN tbl2) as a Subquery, but it's not really a "derived table",
697    as it doesn't introduce a new scope. If an alias is present, it shadows all names
698    under the Subquery, so that's one exception to this rule.
699    """
700    return isinstance(expression, exp.Subquery) and bool(
701        expression.alias or isinstance(expression.this, exp.UNWRAPPED_QUERIES)
702    )
703
704
705def _is_from_or_join(expression: exp.Expression) -> bool:
706    """
707    Determine if `expression` is the FROM or JOIN clause of a SELECT statement.
708    """
709    parent = expression.parent
710
711    # Subqueries can be arbitrarily nested
712    while isinstance(parent, exp.Subquery):
713        parent = parent.parent
714
715    return isinstance(parent, (exp.From, exp.Join))
716
717
718def _traverse_tables(scope):
719    sources = {}
720
721    # Traverse FROMs, JOINs, and LATERALs in the order they are defined
722    expressions = []
723    from_ = scope.expression.args.get("from")
724    if from_:
725        expressions.append(from_.this)
726
727    for join in scope.expression.args.get("joins") or []:
728        expressions.append(join.this)
729
730    if isinstance(scope.expression, exp.Table):
731        expressions.append(scope.expression)
732
733    expressions.extend(scope.expression.args.get("laterals") or [])
734
735    for expression in expressions:
736        if isinstance(expression, exp.Final):
737            expression = expression.this
738        if isinstance(expression, exp.Table):
739            table_name = expression.name
740            source_name = expression.alias_or_name
741
742            if table_name in scope.sources and not expression.db:
743                # This is a reference to a parent source (e.g. a CTE), not an actual table, unless
744                # it is pivoted, because then we get back a new table and hence a new source.
745                pivots = expression.args.get("pivots")
746                if pivots:
747                    sources[pivots[0].alias] = expression
748                else:
749                    sources[source_name] = scope.sources[table_name]
750            elif source_name in sources:
751                sources[find_new_name(sources, table_name)] = expression
752            else:
753                sources[source_name] = expression
754
755            # Make sure to not include the joins twice
756            if expression is not scope.expression:
757                expressions.extend(join.this for join in expression.args.get("joins") or [])
758
759            continue
760
761        if not isinstance(expression, exp.DerivedTable):
762            continue
763
764        if isinstance(expression, exp.UDTF):
765            lateral_sources = sources
766            scope_type = ScopeType.UDTF
767            scopes = scope.udtf_scopes
768        elif _is_derived_table(expression):
769            lateral_sources = None
770            scope_type = ScopeType.DERIVED_TABLE
771            scopes = scope.derived_table_scopes
772            expressions.extend(join.this for join in expression.args.get("joins") or [])
773        else:
774            # Makes sure we check for possible sources in nested table constructs
775            expressions.append(expression.this)
776            expressions.extend(join.this for join in expression.args.get("joins") or [])
777            continue
778
779        child_scope = None
780
781        for child_scope in _traverse_scope(
782            scope.branch(
783                expression,
784                lateral_sources=lateral_sources,
785                outer_columns=expression.alias_column_names,
786                scope_type=scope_type,
787            )
788        ):
789            yield child_scope
790
791            # Tables without aliases will be set as ""
792            # This shouldn't be a problem once qualify_columns runs, as it adds aliases on everything.
793            # Until then, this means that only a single, unaliased derived table is allowed (rather,
794            # the latest one wins.
795            sources[_get_source_alias(expression)] = child_scope
796
797        # append the final child_scope yielded
798        if child_scope:
799            scopes.append(child_scope)
800            scope.table_scopes.append(child_scope)
801
802    scope.sources.update(sources)
803
804
805def _traverse_subqueries(scope):
806    for subquery in scope.subqueries:
807        top = None
808        for child_scope in _traverse_scope(scope.branch(subquery, scope_type=ScopeType.SUBQUERY)):
809            yield child_scope
810            top = child_scope
811        scope.subquery_scopes.append(top)
812
813
814def _traverse_udtfs(scope):
815    if isinstance(scope.expression, exp.Unnest):
816        expressions = scope.expression.expressions
817    elif isinstance(scope.expression, exp.Lateral):
818        expressions = [scope.expression.this]
819    else:
820        expressions = []
821
822    sources = {}
823    for expression in expressions:
824        if _is_derived_table(expression):
825            top = None
826            for child_scope in _traverse_scope(
827                scope.branch(
828                    expression,
829                    scope_type=ScopeType.SUBQUERY,
830                    outer_columns=expression.alias_column_names,
831                )
832            ):
833                yield child_scope
834                top = child_scope
835                sources[_get_source_alias(expression)] = child_scope
836
837            scope.subquery_scopes.append(top)
838
839    scope.sources.update(sources)
840
841
842def walk_in_scope(expression, bfs=True, prune=None):
843    """
844    Returns a generator object which visits all nodes in the syntrax tree, stopping at
845    nodes that start child scopes.
846
847    Args:
848        expression (exp.Expression):
849        bfs (bool): if set to True the BFS traversal order will be applied,
850            otherwise the DFS traversal will be used instead.
851        prune ((node, parent, arg_key) -> bool): callable that returns True if
852            the generator should stop traversing this branch of the tree.
853
854    Yields:
855        tuple[exp.Expression, Optional[exp.Expression], str]: node, parent, arg key
856    """
857    # We'll use this variable to pass state into the dfs generator.
858    # Whenever we set it to True, we exclude a subtree from traversal.
859    crossed_scope_boundary = False
860
861    for node in expression.walk(
862        bfs=bfs, prune=lambda n: crossed_scope_boundary or (prune and prune(n))
863    ):
864        crossed_scope_boundary = False
865
866        yield node
867
868        if node is expression:
869            continue
870
871        if (
872            isinstance(node, exp.CTE)
873            or (
874                isinstance(node.parent, (exp.From, exp.Join, exp.Subquery))
875                and _is_derived_table(node)
876            )
877            or (isinstance(node.parent, exp.UDTF) and isinstance(node, exp.Query))
878            or isinstance(node, exp.UNWRAPPED_QUERIES)
879        ):
880            crossed_scope_boundary = True
881
882            if isinstance(node, (exp.Subquery, exp.UDTF)):
883                # The following args are not actually in the inner scope, so we should visit them
884                for key in ("joins", "laterals", "pivots"):
885                    for arg in node.args.get(key) or []:
886                        yield from walk_in_scope(arg, bfs=bfs)
887
888
889def find_all_in_scope(expression, expression_types, bfs=True):
890    """
891    Returns a generator object which visits all nodes in this scope and only yields those that
892    match at least one of the specified expression types.
893
894    This does NOT traverse into subscopes.
895
896    Args:
897        expression (exp.Expression):
898        expression_types (tuple[type]|type): the expression type(s) to match.
899        bfs (bool): True to use breadth-first search, False to use depth-first.
900
901    Yields:
902        exp.Expression: nodes
903    """
904    for expression in walk_in_scope(expression, bfs=bfs):
905        if isinstance(expression, tuple(ensure_collection(expression_types))):
906            yield expression
907
908
909def find_in_scope(expression, expression_types, bfs=True):
910    """
911    Returns the first node in this scope which matches at least one of the specified types.
912
913    This does NOT traverse into subscopes.
914
915    Args:
916        expression (exp.Expression):
917        expression_types (tuple[type]|type): the expression type(s) to match.
918        bfs (bool): True to use breadth-first search, False to use depth-first.
919
920    Returns:
921        exp.Expression: the node which matches the criteria or None if no node matching
922        the criteria was found.
923    """
924    return next(find_all_in_scope(expression, expression_types, bfs=bfs), None)
925
926
927def _get_source_alias(expression):
928    alias_arg = expression.args.get("alias")
929    alias_name = expression.alias
930
931    if not alias_name and isinstance(alias_arg, exp.TableAlias) and len(alias_arg.columns) == 1:
932        alias_name = alias_arg.columns[0].name
933
934    return alias_name