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from sqlglot import alias, exp
from sqlglot.errors import OptimizeError
from sqlglot.optimizer.scope import traverse_scope
from sqlglot.schema import ensure_schema
def isolate_table_selects(expression, schema=None):
schema = ensure_schema(schema)
for scope in traverse_scope(expression):
if len(scope.selected_sources) == 1:
continue
for _, source in scope.selected_sources.values():
if not isinstance(source, exp.Table) or not schema.column_names(source):
continue
if not source.alias:
raise OptimizeError("Tables require an alias. Run qualify_tables optimization.")
source.replace(
exp.select("*")
.from_(
alias(source.copy(), source.name or source.alias, table=True),
copy=False,
)
.subquery(source.alias, copy=False)
)
return expression
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