数据库上的浮点数舍入

Question

我有以下df：

df
          Process Commodity Direction  ratio  ratio-min
0      Coal plant      Coal        In   1.00        NaN
1      Coal plant      Elec       Out   0.40        NaN
2      Coal plant       CO2       Out   0.30        NaN
3   Lignite plant   Lignite        In   1.00        NaN
4   Lignite plant      Elec       Out   0.40        NaN
5   Lignite plant       CO2       Out   0.40        NaN
6       Gas plant       Gas        In   1.00        NaN
7       Gas plant      Elec       Out   0.60        NaN
8       Gas plant       CO2       Out   0.20        NaN
9   Biomass plant   Biomass        In   1.00        NaN
10  Biomass plant      Elec       Out   0.35        NaN
11  Biomass plant       CO2       Out   0.00        NaN
12      Wind park      Wind        In   1.00        NaN
13      Wind park      Elec       Out   1.00        NaN
14    Hydro plant     Hydro        In   1.00        NaN
15    Hydro plant      Elec       Out   1.00        NaN
16  Photovoltaics     Solar        In   1.00        NaN
17  Photovoltaics      Elec       Out   1.00        NaN

正如您所见，ratio值是浮点数。

我正在尝试使用sqlalchemy将此数据帧发送到数据库。

我在这里设置表格：

import sqlalchemy as sa

table = sa.Table(table_name,
                 metadata,
                 sa.Column('index', sa.Integer, primary_key=True, autoincrement=True, nullable=False),
                 sa.Column('Process', sa.VARCHAR(50)),
                 sa.Column('Commodity', sa.VARCHAR(50)),
                 sa.Column('Direction', sa.VARCHAR(50)),
                 sa.Column('ratio', sa.Float(10)),
                 sa.Column('ratio-min', sa.Float(10)),
                 schema=schema_name)

然后我通过以下方式将表格发送到数据库：df.to_sql(table_name, engine, schema=schema_name, if_exists='replace')

问题是，当我检查数据库时，ratio的所有值都以某种方式舍入。以下是我从数据库获得的内容（在数据库中也是相同的舍入值）

          Process Commodity Direction  ratio ratio-min
0      Coal plant      Coal        In    1.0      None
1      Coal plant      Elec       Out    0.0      None
2      Coal plant       CO2       Out    0.0      None
3   Lignite plant   Lignite        In    1.0      None
4   Lignite plant      Elec       Out    0.0      None
5   Lignite plant       CO2       Out    0.0      None
6       Gas plant       Gas        In    1.0      None
7       Gas plant      Elec       Out    1.0      None
8       Gas plant       CO2       Out    0.0      None
9   Biomass plant   Biomass        In    1.0      None
10  Biomass plant      Elec       Out    0.0      None
11  Biomass plant       CO2       Out    0.0      None
12      Wind park      Wind        In    1.0      None
13      Wind park      Elec       Out    1.0      None
14    Hydro plant     Hydro        In    1.0      None
15    Hydro plant      Elec       Out    1.0      None
16  Photovoltaics     Solar        In    1.0      None
17  Photovoltaics      Elec       Out    1.0      None

我怎么能阻止to_sql围绕我的ratio值？

Answer 1

您可以通过指定列的数据类型来解决此问题，如下所示：

from sqlalchemy.types import Float

然后加

dtype={'ratio': Float()}

对于df.to_sql的论点：

df.to_sql(table_name, engine, schema=schema_name, if_exists='replace', dtype={'ratio': Float()})

参数dtype是一个字典，它将列名作为键，数据类型作为值。这应该可以防止你的ratio值被舍入。