dataframe_pandas.py

# -----------------------------------------------------------------------------
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#
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# See the License for the specific language governing permissions and
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# -----------------------------------------------------------------------------

# -----------------------------------------------------------------------------
# dataframe_pandas.py
#
# Shows how to use connection.fetch_df_all() and connection.fetch_df_batches()
# to create Pandas dataframes.
# -----------------------------------------------------------------------------

import pandas
import pyarrow

import oracledb
import sample_env

# determine whether to use python-oracledb thin mode or thick mode
if not sample_env.get_is_thin():
    oracledb.init_oracle_client(lib_dir=sample_env.get_oracle_client())

connection = oracledb.connect(
    user=sample_env.get_main_user(),
    password=sample_env.get_main_password(),
    dsn=sample_env.get_connect_string(),
    params=sample_env.get_connect_params(),
)

SQL = "select id, name from SampleQueryTab order by id"

# -----------------------------------------------------------------------------
#
# Fetching all records

# Get an OracleDataFrame.
# Adjust arraysize to tune the query fetch performance
odf = connection.fetch_df_all(statement=SQL, arraysize=100)

# Get a Pandas DataFrame from the data
df = pyarrow.Table.from_arrays(
    odf.column_arrays(), names=odf.column_names()
).to_pandas()

# Perform various Pandas operations on the DataFrame

print("Columns:")
print(df.columns)

print("\nDataframe description:")
print(df.describe())

print("\nLast three rows:")
print(df.tail(3))

print("\nTransform:")
print(df.T)

# -----------------------------------------------------------------------------
#
# Batch record fetching
#
# Note that since this particular example ends up with all query rows being
# held in memory, it would be more efficient to use fetch_df_all() as shown
# above.

print("\nFetching in batches:")
df = pandas.DataFrame()

# Tune 'size' for your data set. Here it is small to show the batch fetch
# behavior on the sample table.
for odf in connection.fetch_df_batches(statement=SQL, size=10):
    df_b = pyarrow.Table.from_arrays(
        odf.column_arrays(), names=odf.column_names()
    ).to_pandas()
    print(f"Appending {df_b.shape[0]} rows")
    df = pandas.concat([df, df_b], ignore_index=True)

r, c = df.shape
print(f"{r} rows, {c} columns")

print("\nLast three rows:")
print(df.tail(3))