获取Ibis表达式的查询计划

Question

我正在尝试使用抛出错误的

con.explain

接口从 DuckDB 后端获取 Ibis 表达式的查询计划。我是否正确使用了

con.explain

功能？

def init_ddb_from_csv(db_filename, tablename, csv_filename, **kwargs):
    """
    Load from the csv file into a DuckDB database.
    
    db_filename: Name of the database
    tablename: Table to load to
    csv_filename: CSV file to load from
    **kwargs: Options for DuckDB's read_csv function, see https://duckdb.org/docs/data/csv/overview
    """
    import duckdb
    duckdb_con = duckdb.connect(db_filename)
    read_csv_args_list = ["'{}'".format(csv_filename)]
    for key, value in kwargs.items():
        read_csv_args_list.append("{0} = {1}".format(key, value))
    read_csv_args = ','.join(read_csv_args_list)
    sql_stmt = "CREATE TABLE {} AS SELECT * FROM read_csv({}, AUTO_DETECT=TRUE)".format(tablename, read_csv_args)
    print(sql_stmt)
    duckdb_con.sql(sql_stmt)
    duckdb_con.close()

dbname = "us_accidents.db"
tablename = "accidents"
csv_filename = "US_Accidents_Dec21_updated.csv"
init_ddb_from_csv(dbname, tablename, csv_filename)

con = ibis.duckdb.connect(dbname)
table = con.table(tablename)
con.explain(table.head())

抛出以下错误：

AttributeError                            Traceback (most recent call last)
File ~/workspace/csv/VENV/lib/python3.8/site-packages/sqlalchemy/engine/base.py:1408, in Connection.execute(self, statement, parameters, execution_options)
   1407 try:
-> 1408     meth = statement._execute_on_connection
   1409 except AttributeError as err:

AttributeError: 'str' object has no attribute '_execute_on_connection'

The above exception was the direct cause of the following exception:

ObjectNotExecutableError                  Traceback (most recent call last)
Cell In[29], line 1
----> 1 con.explain(table.head())

File ~/workspace/csv/VENV/lib/python3.8/site-packages/ibis/backends/base/sql/__init__.py:373, in BaseSQLBackend.explain(self, expr, params)
    369     query = expr
    371 statement = f'EXPLAIN {query}'
--> 373 with self._safe_raw_sql(statement) as cur:
    374     result = self._get_list(cur)
    376 return '\n'.join(['Query:', util.indent(query, 2), '', *result])

File /usr/lib/python3.8/contextlib.py:113, in _GeneratorContextManager.__enter__(self)
    111 del self.args, self.kwds, self.func
    112 try:
--> 113     return next(self.gen)
    114 except StopIteration:
    115     raise RuntimeError("generator didn't yield") from None

File ~/workspace/csv/VENV/lib/python3.8/site-packages/ibis/backends/base/sql/alchemy/__init__.py:130, in BaseAlchemyBackend._safe_raw_sql(self, *args, **kwargs)
    127 @contextlib.contextmanager
    128 def _safe_raw_sql(self, *args, **kwargs):
    129     with self.begin() as con:
--> 130         yield con.execute(*args, **kwargs)

File ~/workspace/csv/VENV/lib/python3.8/site-packages/sqlalchemy/engine/base.py:1410, in Connection.execute(self, statement, parameters, execution_options)
   1408     meth = statement._execute_on_connection
   1409 except AttributeError as err:
-> 1410     raise exc.ObjectNotExecutableError(statement) from err
   1411 else:
   1412     return meth(
   1413         self,
   1414         distilled_parameters,
   1415         execution_options or NO_OPTIONS,
   1416     )

ObjectNotExecutableError: Not an executable object: 'EXPLAIN SELECT t0."ID", t0."Severity", t0."Start_Time", t0."End_Time", t0."Start_Lat", t0."Start_Lng", t0."End_Lat", t0."End_Lng", t0."Distance(mi)", t0."Description", t0."Number", t0."Street", t0."Side", t0."City", t0."County", t0."State", t0."Zipcode", t0."Country", t0."Timezone", t0."Airport_Code", t0."Weather_Timestamp", t0."Temperature(F)", t0."Wind_Chill(F)", t0."Humidity(%)", t0."Pressure(in)", t0."Visibility(mi)", t0."Wind_Direction", t0."Wind_Speed(mph)", t0."Precipitation(in)", t0."Weather_Condition", t0."Amenity", t0."Bump", t0."Crossing", t0."Give_Way", t0."Junction", t0."No_Exit", t0."Railway", t0."Roundabout", t0."Station", t0."Stop", t0."Traffic_Calming", t0."Traffic_Signal", t0."Turning_Loop", t0."Sunrise_Sunset", t0."Civil_Twilight", t0."Nautical_Twilight", t0."Astronomical_Twilight" \nFROM accidents AS t0\n LIMIT :param_1'

Answer 1

很抱歉这里的回复很慢——我建议打开一个 GitHub 问题，我们不会经常错过这些问题！

我也看到了这一点——检查文档，我能找到的唯一参考是在 v0.4.0 的发行说明中为 Impala 后端添加了此方法。我猜这是当时的遗留物，没有为任何其他后端实现，但可能是错误的。我会请更有知识的人来检查一下！

发布说明提及：https://ibis-project.org/release_notes/?h=release#04-2015-08-14