Edition-Based Redefinition lets an application be upgraded while users keep running the old version. Editionable objects such as PL/SQL units, views and synonyms exist in multiple editions at once; each session sees one edition. Tables are not editionable, so editioning views present a per-edition column layout over them, and crossedition triggers keep old and new column representations in step while both versions are live. Enabling editions for a schema is irreversible.

Migrations care because none of the Azure targets has editions. Zero-downtime application upgrades must be redesigned around application-tier blue-green deployment and schema versioning. Editioning views also complicate the object inventory: the "tables" an application uses may be views over physically renamed columns, and conversion tools see both layers.

The feature arrived with 11g Release 2 and is fully supported and not deprecated.

Edition-Based Redefinition, born in 11.2, was a PL/SQL feature devoted to online upgrades. It let two versions of code objects and editioning views coexist, keeping old and new arrangements politely in parallel.

Its passage to Azure was blocked because neither SQL Server nor Azure SQL has editions. Session-level edition switching, one of its distinguishing habits, cannot be reproduced.

It is survived by Azure SQL Database, where it lives on not at all. The nearest practice uses versioned schemas with synonyms or views repointed at cutover, expand-and-contract table changes, and SSMA-created synonyms for tables, views, procedures, and functions.