Streams
Streams are logical objects that capture data changes in underlying sources, including the previously mentioned objects (physical tables, views, and external and directory tables). Whenever a DML operation occurs in the source object, a stream tracks the changes (inserts, deletions, and the before/after images of updates). Streams achieve this through an offset storage technique—logically taking an initial snapshot of data and then tracking changes through metadata columns. Although a stream can be queried like a table, it is not a separate object and does not contain table data.
When a stream is created, metadata columns are tacked onto the source object and begin tracking changes. The following table describes the metadata fields and their contents:
Figure 4.4 – Stream metadata columns
The following command creates a stream on a table:
CREATE STREAM <stream_name> ON TABLE <table_name>
