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from __future__ import annotations
import itertools
import math
import typing as t
from sqlglot import alias, exp
from sqlglot.errors import UnsupportedError
from sqlglot.optimizer.eliminate_joins import join_condition
class Plan:
def __init__(self, expression: exp.Expression) -> None:
self.expression = expression.copy()
self.root = Step.from_expression(self.expression)
self._dag: t.Dict[Step, t.Set[Step]] = {}
@property
def dag(self) -> t.Dict[Step, t.Set[Step]]:
if not self._dag:
dag: t.Dict[Step, t.Set[Step]] = {}
nodes = {self.root}
while nodes:
node = nodes.pop()
dag[node] = set()
for dep in node.dependencies:
dag[node].add(dep)
nodes.add(dep)
self._dag = dag
return self._dag
@property
def leaves(self) -> t.Iterator[Step]:
return (node for node, deps in self.dag.items() if not deps)
def __repr__(self) -> str:
return f"Plan\n----\n{repr(self.root)}"
class Step:
@classmethod
def from_expression(
cls, expression: exp.Expression, ctes: t.Optional[t.Dict[str, Step]] = None
) -> Step:
"""
Builds a DAG of Steps from a SQL expression so that it's easier to execute in an engine.
Note: the expression's tables and subqueries must be aliased for this method to work. For
example, given the following expression:
SELECT
x.a,
SUM(x.b)
FROM x AS x
JOIN y AS y
ON x.a = y.a
GROUP BY x.a
the following DAG is produced (the expression IDs might differ per execution):
- Aggregate: x (4347984624)
Context:
Aggregations:
- SUM(x.b)
Group:
- x.a
Projections:
- x.a
- "x".""
Dependencies:
- Join: x (4347985296)
Context:
y:
On: x.a = y.a
Projections:
Dependencies:
- Scan: x (4347983136)
Context:
Source: x AS x
Projections:
- Scan: y (4343416624)
Context:
Source: y AS y
Projections:
Args:
expression: the expression to build the DAG from.
ctes: a dictionary that maps CTEs to their corresponding Step DAG by name.
Returns:
A Step DAG corresponding to `expression`.
"""
ctes = ctes or {}
with_ = expression.args.get("with")
# CTEs break the mold of scope and introduce themselves to all in the context.
if with_:
ctes = ctes.copy()
for cte in with_.expressions:
step = Step.from_expression(cte.this, ctes)
step.name = cte.alias
ctes[step.name] = step # type: ignore
from_ = expression.args.get("from")
if isinstance(expression, exp.Select) and from_:
from_ = from_.expressions
if len(from_) > 1:
raise UnsupportedError(
"Multi-from statements are unsupported. Run it through the optimizer"
)
step = Scan.from_expression(from_[0], ctes)
elif isinstance(expression, exp.Union):
step = SetOperation.from_expression(expression, ctes)
else:
step = Scan()
joins = expression.args.get("joins")
if joins:
join = Join.from_joins(joins, ctes)
join.name = step.name
join.add_dependency(step)
step = join
projections = [] # final selects in this chain of steps representing a select
operands = {} # intermediate computations of agg funcs eg x + 1 in SUM(x + 1)
aggregations = []
sequence = itertools.count()
def extract_agg_operands(expression):
for agg in expression.find_all(exp.AggFunc):
for operand in agg.unnest_operands():
if isinstance(operand, exp.Column):
continue
if operand not in operands:
operands[operand] = f"_a_{next(sequence)}"
operand.replace(exp.column(operands[operand], quoted=True))
for e in expression.expressions:
if e.find(exp.AggFunc):
projections.append(exp.column(e.alias_or_name, step.name, quoted=True))
aggregations.append(e)
extract_agg_operands(e)
else:
projections.append(e)
where = expression.args.get("where")
if where:
step.condition = where.this
group = expression.args.get("group")
if group or aggregations:
aggregate = Aggregate()
aggregate.source = step.name
aggregate.name = step.name
having = expression.args.get("having")
if having:
extract_agg_operands(having)
aggregate.condition = having.this
aggregate.operands = tuple(
alias(operand, alias_) for operand, alias_ in operands.items()
)
aggregate.aggregations = aggregations
# give aggregates names and replace projections with references to them
aggregate.group = {
f"_g{i}": e for i, e in enumerate(group.expressions if group else [])
}
for projection in projections:
for i, e in aggregate.group.items():
for child, *_ in projection.walk():
if child == e:
child.replace(exp.column(i, step.name))
aggregate.add_dependency(step)
step = aggregate
order = expression.args.get("order")
if order:
sort = Sort()
sort.name = step.name
sort.key = order.expressions
sort.add_dependency(step)
step = sort
step.projections = projections
if isinstance(expression, exp.Select) and expression.args.get("distinct"):
distinct = Aggregate()
distinct.source = step.name
distinct.name = step.name
distinct.group = {
e.alias_or_name: exp.column(col=e.alias_or_name, table=step.name)
for e in projections or expression.expressions
}
distinct.add_dependency(step)
step = distinct
limit = expression.args.get("limit")
if limit:
step.limit = int(limit.text("expression"))
return step
def __init__(self) -> None:
self.name: t.Optional[str] = None
self.dependencies: t.Set[Step] = set()
self.dependents: t.Set[Step] = set()
self.projections: t.Sequence[exp.Expression] = []
self.limit: float = math.inf
self.condition: t.Optional[exp.Expression] = None
def add_dependency(self, dependency: Step) -> None:
self.dependencies.add(dependency)
dependency.dependents.add(self)
def __repr__(self) -> str:
return self.to_s()
def to_s(self, level: int = 0) -> str:
indent = " " * level
nested = f"{indent} "
context = self._to_s(f"{nested} ")
if context:
context = [f"{nested}Context:"] + context
lines = [
f"{indent}- {self.id}",
*context,
f"{nested}Projections:",
]
for expression in self.projections:
lines.append(f"{nested} - {expression.sql()}")
if self.condition:
lines.append(f"{nested}Condition: {self.condition.sql()}")
if self.limit is not math.inf:
lines.append(f"{nested}Limit: {self.limit}")
if self.dependencies:
lines.append(f"{nested}Dependencies:")
for dependency in self.dependencies:
lines.append(" " + dependency.to_s(level + 1))
return "\n".join(lines)
@property
def type_name(self) -> str:
return self.__class__.__name__
@property
def id(self) -> str:
name = self.name
name = f" {name}" if name else ""
return f"{self.type_name}:{name} ({id(self)})"
def _to_s(self, _indent: str) -> t.List[str]:
return []
class Scan(Step):
@classmethod
def from_expression(
cls, expression: exp.Expression, ctes: t.Optional[t.Dict[str, Step]] = None
) -> Step:
table = expression
alias_ = expression.alias_or_name
if isinstance(expression, exp.Subquery):
table = expression.this
step = Step.from_expression(table, ctes)
step.name = alias_
return step
step = Scan()
step.name = alias_
step.source = expression
if ctes and table.name in ctes:
step.add_dependency(ctes[table.name])
return step
def __init__(self) -> None:
super().__init__()
self.source: t.Optional[exp.Expression] = None
def _to_s(self, indent: str) -> t.List[str]:
return [f"{indent}Source: {self.source.sql() if self.source else '-static-'}"] # type: ignore
class Join(Step):
@classmethod
def from_joins(
cls, joins: t.Iterable[exp.Join], ctes: t.Optional[t.Dict[str, Step]] = None
) -> Step:
step = Join()
for join in joins:
source_key, join_key, condition = join_condition(join)
step.joins[join.this.alias_or_name] = {
"side": join.side,
"join_key": join_key,
"source_key": source_key,
"condition": condition,
}
step.add_dependency(Scan.from_expression(join.this, ctes))
return step
def __init__(self) -> None:
super().__init__()
self.joins: t.Dict[str, t.Dict[str, t.List[str] | exp.Expression]] = {}
def _to_s(self, indent: str) -> t.List[str]:
lines = []
for name, join in self.joins.items():
lines.append(f"{indent}{name}: {join['side']}")
if join.get("condition"):
lines.append(f"{indent}On: {join['condition'].sql()}") # type: ignore
return lines
class Aggregate(Step):
def __init__(self) -> None:
super().__init__()
self.aggregations: t.List[exp.Expression] = []
self.operands: t.Tuple[exp.Expression, ...] = ()
self.group: t.Dict[str, exp.Expression] = {}
self.source: t.Optional[str] = None
def _to_s(self, indent: str) -> t.List[str]:
lines = [f"{indent}Aggregations:"]
for expression in self.aggregations:
lines.append(f"{indent} - {expression.sql()}")
if self.group:
lines.append(f"{indent}Group:")
for expression in self.group.values():
lines.append(f"{indent} - {expression.sql()}")
if self.condition:
lines.append(f"{indent}Having:")
lines.append(f"{indent} - {self.condition.sql()}")
if self.operands:
lines.append(f"{indent}Operands:")
for expression in self.operands:
lines.append(f"{indent} - {expression.sql()}")
return lines
class Sort(Step):
def __init__(self) -> None:
super().__init__()
self.key = None
def _to_s(self, indent: str) -> t.List[str]:
lines = [f"{indent}Key:"]
for expression in self.key: # type: ignore
lines.append(f"{indent} - {expression.sql()}")
return lines
class SetOperation(Step):
def __init__(
self,
op: t.Type[exp.Expression],
left: str | None,
right: str | None,
distinct: bool = False,
) -> None:
super().__init__()
self.op = op
self.left = left
self.right = right
self.distinct = distinct
@classmethod
def from_expression(
cls, expression: exp.Expression, ctes: t.Optional[t.Dict[str, Step]] = None
) -> Step:
assert isinstance(expression, exp.Union)
left = Step.from_expression(expression.left, ctes)
right = Step.from_expression(expression.right, ctes)
step = cls(
op=expression.__class__,
left=left.name,
right=right.name,
distinct=bool(expression.args.get("distinct")),
)
step.add_dependency(left)
step.add_dependency(right)
return step
def _to_s(self, indent: str) -> t.List[str]:
lines = []
if self.distinct:
lines.append(f"{indent}Distinct: {self.distinct}")
return lines
@property
def type_name(self) -> str:
return self.op.__name__
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