Executing statements in Oracle

Warning

Methods below read all the rows returned from DB to Spark driver memory, and then convert them to DataFrame.

Do NOT use them to read large amounts of data. Use DBReader or Oracle.sql instead.

How to

There are 2 ways to execute some statement in Oracle

Use Oracle.fetch

Use this method to execute some SELECT query which returns small number or rows, like reading Oracle config, or reading data from some reference table. Method returns Spark DataFrame.

Method accepts JDBCOptions.

Connection opened using this method should be then closed with connection.close() or with connection:.

Warning

Please take into account Oracle <-> Spark type mapping.

Syntax support

This method supports any query syntax supported by Oracle, like:

• ✅︎ SELECT ... FROM ...

• ✅︎ WITH alias AS (...) SELECT ...

• ✅︎ SELECT func(arg1, arg2) FROM DUAL - call function

• ✅︎ SHOW ...

• ❌ SET ...; SELECT ...; - multiple statements not supported

Examples

from onetl.connection import Oracle

oracle = Oracle(...)

df = oracle.fetch(
    "SELECT value FROM some.reference_table WHERE key = 'some_constant'",
    options=Oracle.JDBCOptions(query_timeout=10),
)
oracle.close()
value = df.collect()[0][0]  # get value from first row and first column

Use Oracle.execute

Use this method to execute DDL and DML operations. Each method call runs operation in a separated transaction, and then commits it.

Method accepts JDBCOptions.

Connection opened using this method should be then closed with connection.close() or with connection:.

Syntax support

This method supports any query syntax supported by Oracle, like:

• ✅︎ CREATE TABLE ..., CREATE VIEW ...

• ✅︎ ALTER ...

• ✅︎ INSERT INTO ... SELECT ..., UPDATE ..., DELETE ..., and so on

• ✅︎ DROP TABLE ..., DROP VIEW ..., and so on

• ✅︎ CALL procedure(arg1, arg2) ... or {call procedure(arg1, arg2)} - special syntax for calling procedure

• ✅︎ DECLARE ... BEGIN ... END - execute PL/SQL statement

• ✅︎ other statements not mentioned here

• ❌ SET ...; SELECT ...; - multiple statements not supported

Examples

from onetl.connection import Oracle

oracle = Oracle(...)

with oracle:
    # automatically close connection after exiting this context manager
    oracle.execute("DROP TABLE schema.table")
    oracle.execute(
        """
        CREATE TABLE schema.table AS (
            id bigint GENERATED ALWAYS AS IDENTITY,
            key VARCHAR2(4000),
            value NUMBER
        )
        """,
        options=Oracle.JDBCOptions(query_timeout=10),
    )

Options

pydantic model onetl.connection.db_connection.jdbc_mixin.options.JDBCOptions

Generic options, related to specific JDBC driver.

Note

You can pass any value supported by underlying JDBC driver class, even if it is not mentioned in this documentation.

field query_timeout: int | None = None (alias 'queryTimeout')

The number of seconds the driver will wait for a statement to execute. Zero means there is no limit.

This option depends on driver implementation, some drivers can check the timeout of each query instead of an entire JDBC batch.

field fetchsize: int | None = None

How many rows to fetch per round trip.

Tuning this option can influence performance of reading.

Warning

Default value depends on driver. For example, Oracle has default fetchsize=10.