Updating an oracle sequence nextval
The may be placed on any column as a “default” generator to be used during INSERT operations, and can also be configured to fire off during UPDATE operations if desired.
are invoked explicitly by SQLAlchemy when an INSERT or UPDATE statement occurs, typically rendered inline within the DML statement except in certain cases listed below.In particular, the object, which is considered to be a special case of “column default”.It only has an effect on databases which have explicit support for sequences, which currently includes Postgre SQL, Oracle, and Firebird.If the statement , or as SQL expressions which are rendered directly within an INSERT or UPDATE statement emitted by SQLAlchemy; they may also be client-side Python functions or constant values which are invoked by SQLAlchemy before data is passed to the database.Above, the value “12” will be bound as the column value during an INSERT if no other value is supplied.This is different than a “server side” default, which is part of the table’s DDL definition, e.g.
as part of the “CREATE TABLE” statement, which are likely more common.
Column INSERT and UPDATE defaults refer to functions that create a default value for a particular column in a row as an INSERT or UPDATE statement is proceeding against that row, in the case where no value was provided to the INSERT or UPDATE statement for that column.
That is, if a table has a column called “timestamp”, and an INSERT statement proceeds which does not include a value for this column, an INSERT default would create a new value, such as the current time, that is used as the value to be INSERTed into the “timestamp” column.
Instead, it marks the column as one that will have a new value populated by the database during the process of an INSERT or UPDATE statement, and for supporting databases may be used to indicate that the column should be part of a RETURNING or OUTPUT clause for the statement.
Tools such as the SQLAlchemy ORM then make use of this marker in order to know how to get at the value of the column after such an operation.
The syntax for creating a sequence in Oracle is: is the starting value of the sequence, and is the interval between consecutive sequence numbers.