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feat(sql): lower expressions to SQL-like relational operations
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"""Lower the ibis expression graph to a SQL-like relational algebra.""" | ||
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from __future__ import annotations | ||
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from typing import Literal, Optional | ||
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from public import public | ||
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import ibis.expr.datashape as ds | ||
import ibis.expr.datatypes as dt | ||
import ibis.expr.operations as ops | ||
from ibis.common.annotations import attribute | ||
from ibis.common.collections import FrozenDict # noqa: TCH001 | ||
from ibis.common.patterns import Object, replace | ||
from ibis.common.typing import VarTuple # noqa: TCH001 | ||
from ibis.expr.rewrites import p | ||
from ibis.expr.schema import Schema | ||
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@public | ||
class Select(ops.Relation): | ||
"""Relation modelled after SQL's SELECT statement.""" | ||
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parent: ops.Relation | ||
selections: FrozenDict[str, ops.Value] = {} | ||
predicates: VarTuple[ops.Value[dt.Boolean]] = () | ||
sort_keys: VarTuple[ops.SortKey] = () | ||
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@attribute | ||
def values(self): | ||
return self.selections | ||
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@attribute | ||
def schema(self): | ||
return Schema({k: v.dtype for k, v in self.selections.items()}) | ||
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@public | ||
class Window(ops.Value): | ||
"""Window modelled after SQL's window statements.""" | ||
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how: Literal["rows", "range"] | ||
func: ops.Reduction | ops.Analytic | ||
start: Optional[ops.WindowBoundary] = None | ||
end: Optional[ops.WindowBoundary] = None | ||
group_by: VarTuple[ops.Column] = () | ||
order_by: VarTuple[ops.SortKey] = () | ||
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shape = ds.columnar | ||
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@attribute | ||
def dtype(self): | ||
return self.func.dtype | ||
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@replace(p.Project) | ||
def project_to_select(_): | ||
"""Convert a Project node to a Select node.""" | ||
return Select(_.parent, selections=_.values) | ||
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@replace(p.Filter) | ||
def filter_to_select(_): | ||
"""Convert a Filter node to a Select node.""" | ||
return Select(_.parent, selections=_.values, predicates=_.predicates) | ||
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@replace(p.Sort) | ||
def sort_to_select(_): | ||
"""Convert a Sort node to a Select node.""" | ||
return Select(_.parent, selections=_.values, sort_keys=_.keys) | ||
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@replace(p.WindowFunction) | ||
def window_function_to_window(_): | ||
"""Convert a WindowFunction node to a Window node.""" | ||
if isinstance(_.frame, ops.RowsWindowFrame) and _.frame.max_lookback is not None: | ||
raise NotImplementedError("max_lookback is not supported for SQL backends") | ||
return Window( | ||
how=_.frame.how, | ||
func=_.func, | ||
start=_.frame.start, | ||
end=_.frame.end, | ||
group_by=_.frame.group_by, | ||
order_by=_.frame.order_by, | ||
) | ||
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@replace(Object(Select, Object(Select))) | ||
def merge_select_select(_): | ||
"""Merge subsequent Select relations into one. | ||
This rewrites eliminates `_.parent` by merging the outer and the inner | ||
`predicates`, `sort_keys` and keeping the outer `selections`. All selections | ||
from the inner Select are inlined into the outer Select. | ||
""" | ||
# don't merge if either the outer or the inner select has window functions | ||
for v in _.selections.values(): | ||
if v.find(Window, filter=ops.Value): | ||
return _ | ||
for v in _.parent.selections.values(): | ||
if v.find((Window, ops.Unnest), filter=ops.Value): | ||
return _ | ||
for v in _.predicates: | ||
if v.find(ops.ExistsSubquery, filter=ops.Value): | ||
return _ | ||
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subs = {ops.Field(_.parent, k): v for k, v in _.parent.values.items()} | ||
selections = {k: v.replace(subs) for k, v in _.selections.items()} | ||
predicates = tuple(p.replace(subs, filter=ops.Value) for p in _.predicates) | ||
sort_keys = tuple(s.replace(subs) for s in _.sort_keys) | ||
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return Select( | ||
_.parent.parent, | ||
selections=selections, | ||
predicates=_.parent.predicates + predicates, | ||
sort_keys=_.parent.sort_keys + sort_keys, | ||
) | ||
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def sqlize(node): | ||
"""Lower the ibis expression graph to a SQL-like relational algebra.""" | ||
step1 = node.replace( | ||
window_function_to_window | ||
| project_to_select | ||
| filter_to_select | ||
| sort_to_select | ||
) | ||
step2 = step1.replace(merge_select_select) | ||
return step2 |
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from __future__ import annotations | ||
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import ibis | ||
import ibis.expr.datatypes as dt | ||
import ibis.expr.operations as ops | ||
from ibis.backends.base.sqlglot.rewrites import Select, Window, sqlize | ||
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t = ibis.table( | ||
name="t", | ||
schema={ | ||
"a": dt.int64, | ||
"b": dt.string, | ||
"c": dt.double, | ||
"d": dt.boolean, | ||
}, | ||
) | ||
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def test_sqlize(): | ||
expr = t.mutate(e=t.a.fillna(0)).filter(t.a > 0).order_by(t.b).mutate(f=t.a + 1) | ||
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result = sqlize(expr.op()) | ||
expected = Select( | ||
parent=t, | ||
selections={ | ||
"a": t.a, | ||
"b": t.b, | ||
"c": t.c, | ||
"d": t.d, | ||
"e": ops.Coalesce([t.a, 0]), | ||
"f": t.a + 1, | ||
}, | ||
predicates=(t.a > 0,), | ||
sort_keys=(t.b.asc(),), | ||
) | ||
assert result == expected | ||
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def test_sqlize_dont_merge_windows(): | ||
g = t.a.sum().name("g") | ||
h = t.a.cumsum().name("h") | ||
expr = t.mutate(g, h).filter(t.a > 0).select("a", "g", "h") | ||
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result = sqlize(expr.op()) | ||
sel1 = Select( | ||
parent=t, | ||
selections={ | ||
"a": t.a, | ||
"b": t.b, | ||
"c": t.c, | ||
"d": t.d, | ||
"g": Window(how="rows", func=t.a.sum()), | ||
"h": Window( | ||
how="rows", func=t.a.sum(), end=ops.WindowBoundary(0, preceding=False) | ||
), | ||
}, | ||
).to_expr() | ||
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sel2 = Select( | ||
parent=sel1, | ||
selections={ | ||
"a": sel1.a, | ||
"g": sel1.g, | ||
"h": sel1.h, | ||
}, | ||
predicates=(sel1.a > 0,), | ||
) | ||
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assert result == sel2 |