---
id: schema-changes
title: "Schema changes"
---

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## For new data

Apache Druid allows you to provide a new schema for new data without the need to update the schema of any existing data.
It is sufficient to update your supervisor spec, if using [streaming ingestion](../ingestion/index.md#streaming), or to
provide the new schema the next time you do a [batch ingestion](../ingestion/index.md#batch). This is made possible by
the fact that each [segment](../design/segments.md), at the time it is created, stores a
copy of its own schema. Druid reconciles all of these individual segment schemas automatically at query time.

## For existing data

Schema changes are sometimes necessary for existing data. For example, you may want to change the type of a column in
previously-ingested data, or drop a column entirely. Druid handles this using [reindexing](update.md), the same method
it uses to handle updates of existing data. Reindexing involves rewriting all affected segments and can be a
time-consuming operation.