Support for the Oracle database.

DBAPI Support¶

The following dialect/DBAPI options are available. Please refer to individual DBAPI sections for connect information.

• cx-Oracle
• zxJDBC for Jython

Connect Arguments¶

The dialect supports several create_engine() arguments which affect the behavior of the dialect regardless of driver in use.

• use_ansi - Use ANSI JOIN constructs (see the section on Oracle 8). Defaults to True. If False, Oracle-8 compatible constructs are used for joins.
• optimize_limits - defaults to False. see the section on LIMIT/OFFSET.
• use_binds_for_limits - defaults to True. see the section on LIMIT/OFFSET.

Auto Increment Behavior¶

SQLAlchemy Table objects which include integer primary keys are usually assumed to have “autoincrementing” behavior, meaning they can generate their own primary key values upon INSERT. Since Oracle has no “autoincrement” feature, SQLAlchemy relies upon sequences to produce these values. With the Oracle dialect, a sequence must always be explicitly specified to enable autoincrement. This is divergent with the majority of documentation examples which assume the usage of an autoincrement-capable database. To specify sequences, use the sqlalchemy.schema.Sequence object which is passed to a Column construct:

t = Table('mytable', metadata,
      Column('id', Integer, Sequence('id_seq'), primary_key=True),
      Column(...), ...
)

This step is also required when using table reflection, i.e. autoload=True:

t = Table('mytable', metadata,
      Column('id', Integer, Sequence('id_seq'), primary_key=True),
      autoload=True
)

Identifier Casing¶

In Oracle, the data dictionary represents all case insensitive identifier names using UPPERCASE text. SQLAlchemy on the other hand considers an all-lower case identifier name to be case insensitive. The Oracle dialect converts all case insensitive identifiers to and from those two formats during schema level communication, such as reflection of tables and indexes. Using an UPPERCASE name on the SQLAlchemy side indicates a case sensitive identifier, and SQLAlchemy will quote the name - this will cause mismatches against data dictionary data received from Oracle, so unless identifier names have been truly created as case sensitive (i.e. using quoted names), all lowercase names should be used on the SQLAlchemy side.

LIMIT/OFFSET Support¶

Oracle has no support for the LIMIT or OFFSET keywords. SQLAlchemy uses a wrapped subquery approach in conjunction with ROWNUM. The exact methodology is taken from http://www.oracle.com/technology/oramag/oracle/06-sep/o56asktom.html .

There are two options which affect its behavior:

• the “FIRST ROWS()” optimization keyword is not used by default. To enable the usage of this optimization directive, specify optimize_limits=True to create_engine().
• the values passed for the limit/offset are sent as bound parameters. Some users have observed that Oracle produces a poor query plan when the values are sent as binds and not rendered literally. To render the limit/offset values literally within the SQL statement, specify use_binds_for_limits=False to create_engine().

Some users have reported better performance when the entirely different approach of a window query is used, i.e. ROW_NUMBER() OVER (ORDER BY), to provide LIMIT/OFFSET (note that the majority of users don’t observe this). To suit this case the method used for LIMIT/OFFSET can be replaced entirely. See the recipe at http://www.sqlalchemy.org/trac/wiki/UsageRecipes/WindowFunctionsByDefault which installs a select compiler that overrides the generation of limit/offset with a window function.

RETURNING Support¶

The Oracle database supports a limited form of RETURNING, in order to retrieve result sets of matched rows from INSERT, UPDATE and DELETE statements. Oracle’s RETURNING..INTO syntax only supports one row being returned, as it relies upon OUT parameters in order to function. In addition, supported DBAPIs have further limitations (see RETURNING Support).

SQLAlchemy’s “implicit returning” feature, which employs RETURNING within an INSERT and sometimes an UPDATE statement in order to fetch newly generated primary key values and other SQL defaults and expressions, is normally enabled on the Oracle backend. By default, “implicit returning” typically only fetches the value of a single nextval(some_seq) expression embedded into an INSERT in order to increment a sequence within an INSERT statement and get the value back at the same time. To disable this feature across the board, specify implicit_returning=False to create_engine():

engine = create_engine("oracle://scott:tiger@dsn",
                       implicit_returning=False)

Implicit returning can also be disabled on a table-by-table basis as a table option:

# Core Table
my_table = Table("my_table", metadata, ..., implicit_returning=False)


# declarative
class MyClass(Base):
    __tablename__ = 'my_table'
    __table_args__ = {"implicit_returning": False}

ON UPDATE CASCADE¶

Oracle doesn’t have native ON UPDATE CASCADE functionality. A trigger based solution is available at http://asktom.oracle.com/tkyte/update_cascade/index.html .

When using the SQLAlchemy ORM, the ORM has limited ability to manually issue cascading updates - specify ForeignKey objects using the “deferrable=True, initially=’deferred’” keyword arguments, and specify “passive_updates=False” on each relationship().

Oracle 8 Compatibility¶

When Oracle 8 is detected, the dialect internally configures itself to the following behaviors:

• the use_ansi flag is set to False. This has the effect of converting all JOIN phrases into the WHERE clause, and in the case of LEFT OUTER JOIN makes use of Oracle’s (+) operator.
• the NVARCHAR2 and NCLOB datatypes are no longer generated as DDL when the Unicode is used - VARCHAR2 and CLOB are issued instead. This because these types don’t seem to work correctly on Oracle 8 even though they are available. The NVARCHAR and NCLOB types will always generate NVARCHAR2 and NCLOB.
• the “native unicode” mode is disabled when using cx_oracle, i.e. SQLAlchemy encodes all Python unicode objects to “string” before passing in as bind parameters.

Synonym/DBLINK Reflection¶

When using reflection with Table objects, the dialect can optionally search for tables indicated by synonyms, either in local or remote schemas or accessed over DBLINK, by passing the flag oracle_resolve_synonyms=True as a keyword argument to the Table construct:

some_table = Table('some_table', autoload=True,
                            autoload_with=some_engine,
                            oracle_resolve_synonyms=True)

When this flag is set, the given name (such as some_table above) will be searched not just in the ALL_TABLES view, but also within the ALL_SYNONYMS view to see if this name is actually a synonym to another name. If the synonym is located and refers to a DBLINK, the oracle dialect knows how to locate the table’s information using DBLINK syntax(e.g. @dblink).

oracle_resolve_synonyms is accepted wherever reflection arguments are accepted, including methods such as MetaData.reflect() and Inspector.get_columns().

If synonyms are not in use, this flag should be left disabled.

DateTime Compatibility¶

Oracle has no datatype known as DATETIME, it instead has only DATE, which can actually store a date and time value. For this reason, the Oracle dialect provides a type oracle.DATE which is a subclass of DateTime. This type has no special behavior, and is only present as a “marker” for this type; additionally, when a database column is reflected and the type is reported as DATE, the time-supporting oracle.DATE type is used.

Oracle Table Options¶

The CREATE TABLE phrase supports the following options with Oracle in conjunction with the Table construct:

• ON COMMIT:

  Table(
      "some_table", metadata, ...,
      prefixes=['GLOBAL TEMPORARY'], oracle_on_commit='PRESERVE ROWS')

• COMPRESS:

   Table('mytable', metadata, Column('data', String(32)),
       oracle_compress=True)
  
   Table('mytable', metadata, Column('data', String(32)),
       oracle_compress=6)
  
  The ``oracle_compress`` parameter accepts either an integer compression
  level, or ``True`` to use the default compression level.

Oracle Specific Index Options¶

Index('my_index', my_table.c.data, oracle_bitmap=True)

Index('my_index', my_table.c.data, oracle_compress=True)

Index('my_index', my_table.c.data1, my_table.c.data2, unique=True,
       oracle_compress=1)

Oracle Data Types¶

As with all SQLAlchemy dialects, all UPPERCASE types that are known to be valid with Oracle are importable from the top level dialect, whether they originate from sqlalchemy.types or from the local dialect:

from sqlalchemy.dialects.oracle import \
            BFILE, BLOB, CHAR, CLOB, DATE, \
            DOUBLE_PRECISION, FLOAT, INTERVAL, LONG, NCLOB, \
            NUMBER, NVARCHAR, NVARCHAR2, RAW, TIMESTAMP, VARCHAR, \
            VARCHAR2

Types which are specific to Oracle, or have Oracle-specific construction arguments, are as follows:

class sqlalchemy.dialects.oracle.BFILE(length=None)¶

Bases: sqlalchemy.types.LargeBinary

__init__(length=None)¶

inherited from the __init__() method of LargeBinary

Construct a LargeBinary type.

Parameters:	length¶ – optional, a length for the column for use in DDL statements, for those binary types that accept a length, such as the MySQL BLOB type.

class sqlalchemy.dialects.oracle.DATE(timezone=False)¶

Bases: sqlalchemy.types.DateTime

Provide the oracle DATE type.

This type has no special Python behavior, except that it subclasses types.DateTime; this is to suit the fact that the Oracle DATE type supports a time value.

New in version 0.9.4.

__init__(timezone=False)¶

inherited from the __init__() method of DateTime

Construct a new DateTime.

Parameters:	timezone¶ – boolean. If True, and supported by the backend, will produce ‘TIMESTAMP WITH TIMEZONE’. For backends that don’t support timezone aware timestamps, has no effect.

class sqlalchemy.dialects.oracle.DOUBLE_PRECISION(precision=None, scale=None, asdecimal=None)¶

Bases: sqlalchemy.types.Numeric

class sqlalchemy.dialects.oracle.INTERVAL(day_precision=None, second_precision=None)¶

Bases: sqlalchemy.types.TypeEngine

__init__(day_precision=None, second_precision=None)¶

Construct an INTERVAL.

Note that only DAY TO SECOND intervals are currently supported. This is due to a lack of support for YEAR TO MONTH intervals within available DBAPIs (cx_oracle and zxjdbc).

Parameters:	day_precision¶ – the day precision value. this is the number of digits to store for the day field. Defaults to “2” second_precision¶ – the second precision value. this is the number of digits to store for the fractional seconds field. Defaults to “6”.

class sqlalchemy.dialects.oracle.NCLOB(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False)¶

Bases: sqlalchemy.types.Text

__init__(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False)¶

inherited from the __init__() method of String

Create a string-holding type.

Parameters:

length¶ – optional, a length for the column for use in DDL and CAST expressions. May be safely omitted if no CREATE TABLE will be issued. Certain databases may require a length for use in DDL, and will raise an exception when the CREATE TABLE DDL is issued if a VARCHAR with no length is included. Whether the value is interpreted as bytes or characters is database specific. collation¶ – Optional, a column-level collation for use in DDL and CAST expressions. Renders using the COLLATE keyword supported by SQLite, MySQL, and Postgresql. E.g.: >>> from sqlalchemy import cast, select, String >>> print select([cast('some string', String(collation='utf8'))]) SELECT CAST(:param_1 AS VARCHAR COLLATE utf8) AS anon_1 New in version 0.8: Added support for COLLATE to all string types. convert_unicode¶ – When set to True, the String type will assume that input is to be passed as Python unicode objects, and results returned as Python unicode objects. If the DBAPI in use does not support Python unicode (which is fewer and fewer these days), SQLAlchemy will encode/decode the value, using the value of the encoding parameter passed to create_engine() as the encoding. When using a DBAPI that natively supports Python unicode objects, this flag generally does not need to be set. For columns that are explicitly intended to store non-ASCII data, the Unicode or UnicodeText types should be used regardless, which feature the same behavior of convert_unicode but also indicate an underlying column type that directly supports unicode, such as NVARCHAR. For the extremely rare case that Python unicode is to be encoded/decoded by SQLAlchemy on a backend that does natively support Python unicode, the value force can be passed here which will cause SQLAlchemy’s encode/decode services to be used unconditionally. unicode_error¶ – Optional, a method to use to handle Unicode conversion errors. Behaves like the errors keyword argument to the standard library’s string.decode() functions. This flag requires that convert_unicode is set to force - otherwise, SQLAlchemy is not guaranteed to handle the task of unicode conversion. Note that this flag adds significant performance overhead to row-fetching operations for backends that already return unicode objects natively (which most DBAPIs do). This flag should only be used as a last resort for reading strings from a column with varied or corrupted encodings.

class sqlalchemy.dialects.oracle.NUMBER(precision=None, scale=None, asdecimal=None)¶

Bases: sqlalchemy.types.Numeric, sqlalchemy.types.Integer

class sqlalchemy.dialects.oracle.LONG(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False)¶

Bases: sqlalchemy.types.Text

__init__(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False)¶

inherited from the __init__() method of String

Create a string-holding type.

Parameters:

length¶ – optional, a length for the column for use in DDL and CAST expressions. May be safely omitted if no CREATE TABLE will be issued. Certain databases may require a length for use in DDL, and will raise an exception when the CREATE TABLE DDL is issued if a VARCHAR with no length is included. Whether the value is interpreted as bytes or characters is database specific. collation¶ – Optional, a column-level collation for use in DDL and CAST expressions. Renders using the COLLATE keyword supported by SQLite, MySQL, and Postgresql. E.g.: >>> from sqlalchemy import cast, select, String >>> print select([cast('some string', String(collation='utf8'))]) SELECT CAST(:param_1 AS VARCHAR COLLATE utf8) AS anon_1 New in version 0.8: Added support for COLLATE to all string types. convert_unicode¶ – When set to True, the String type will assume that input is to be passed as Python unicode objects, and results returned as Python unicode objects. If the DBAPI in use does not support Python unicode (which is fewer and fewer these days), SQLAlchemy will encode/decode the value, using the value of the encoding parameter passed to create_engine() as the encoding. When using a DBAPI that natively supports Python unicode objects, this flag generally does not need to be set. For columns that are explicitly intended to store non-ASCII data, the Unicode or UnicodeText types should be used regardless, which feature the same behavior of convert_unicode but also indicate an underlying column type that directly supports unicode, such as NVARCHAR. For the extremely rare case that Python unicode is to be encoded/decoded by SQLAlchemy on a backend that does natively support Python unicode, the value force can be passed here which will cause SQLAlchemy’s encode/decode services to be used unconditionally. unicode_error¶ – Optional, a method to use to handle Unicode conversion errors. Behaves like the errors keyword argument to the standard library’s string.decode() functions. This flag requires that convert_unicode is set to force - otherwise, SQLAlchemy is not guaranteed to handle the task of unicode conversion. Note that this flag adds significant performance overhead to row-fetching operations for backends that already return unicode objects natively (which most DBAPIs do). This flag should only be used as a last resort for reading strings from a column with varied or corrupted encodings.

class sqlalchemy.dialects.oracle.RAW(length=None)¶

Bases: sqlalchemy.types._Binary

cx_Oracle¶

Support for the Oracle database via the cx-Oracle driver.

oracle+cx_oracle://user:pass@host:port/dbname[?key=value&key=value...]

engine = create_engine("oracle+cx_oracle://dsn", coerce_to_unicode=True)

from sqlalchemy import text, Unicode
result = conn.execute(
    text("select username from user").columns(username=Unicode))

engine = create_engine("oracle://scott:tiger@dsn",
                       implicit_returning=False)

engine = create_engine("oracle+cx_oracle://dsn", coerce_to_decimal=False)

zxjdbc¶

Support for the Oracle database via the zxJDBC for Jython driver.

oracle+zxjdbc://user:pass@host/dbname