Delta's optional ability to add columns that appear in incoming data to the target table while writing. You switch it on for a single operation using INSERT WITH SCHEMA EVOLUTION, MERGE WITH SCHEMA EVOLUTION or the mergeSchema option, not for the whole session.
Read more: Microsoft Learn
In the Ultra Transcenders books
Each book explains Schema evolution in context, with comparison tables and the common traps.
Terms in this definition
- Architecture Definition Document
A key deliverable bringing together the main architecture artifacts across the four domains for every relevant state: baseline, transition and target. It sets out, in qualitative terms, what the architect intends.
- Event
Table in Log Analytics where entries from Windows event logs are kept.
- SWITCH
Checks one expression against several candidate values, returning whichever result pairs with the match (or a fallback otherwise). Writing SWITCH ( TRUE (), ... ) avoids nested IF chains: whichever condition is first true wins.
- INSERT
Adds fresh rows to a table. You list the target columns and supply a value for each; it is part of Data Manipulation Language (DML).
- MERGE
A SQL command that compares a source with a target table and, depending on whether rows match, inserts, updates or deletes them. Fabric Warehouse supports it as generally available, and Spark SQL offers MERGE INTO for Delta tables.