Updating an oracle sequence nextval
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.
In other words, a sequence can be used to generate primary key values for multiple tables, and the sequence continues even if it is being applied to a different table.
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.
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.
However, the sequence will not be present as the server-side default for the column when CREATE TABLE is emitted.
If we want the sequence to be used as a server-side default, meaning it takes place even if we emit INSERT commands to the table from the SQL command line, we can use the in both the Python-side and server-side default generation contexts ensures that the “primary key fetch” logic works in all cases.
See the API documentation for of a statement is an internal SQLAlchemy object which contains all information about the statement being executed, including its source expression, the parameters associated with it and the cursor.