---
type: concept
x-llmwiki:
  schemaVersion: "0.1"
  contentHash: 0f9b0dac59698744a918404b6398a39707214c98115746c8989dfad0585e18cf
  pageDirectory: concepts
  sources:
    - delta_duplicate_columns_found-error-condition-databricks-on-aws.md
  confidence: 0.95
  provenanceState: extracted
  freshnessStatus: unverified
  aliases:
    - delta-lake-schema-operations-and-duplicate-column-detection
    - Duplicate Column Detection and Delta Lake Schema Operations
    - DLSOADCD
  citations:
    - file: delta_duplicate_columns_found-error-condition-databricks-on-aws.md
title: Delta Lake Schema Operations and Duplicate Column Detection
description: The set of Delta Lake operations (schema changes, data ingestion, partitioning, clustering, table conversion) that trigger duplicate column validation and raise DELTA_DUPLICATE_COLUMNS_FOUND.
tags:
  - delta-lake
  - schema-management
  - data-validation
timestamp: "2026-06-19T15:04:45.592Z"
---

# Delta Lake Schema Operations and Duplicate Column Detection

**Delta Lake Schema Operations and Duplicate Column Detection** refers to the enforcement of unique column names in a [Delta Lake](/concepts/delta-lake.md) table when performing schema modifications, writes, or reads. Delta Lake validates that column names are not duplicated across various schema-related actions, and raises the `DELTA_DUPLICATE_COLUMNS_FOUND` error if duplicates are detected. ^[delta_duplicate_columns_found-error-condition-databricks-on-aws.md]

## The Error

The `DELTA_DUPLICATE_COLUMNS_FOUND` error is a runtime error with SQLSTATE `42711` (syntax error or access rule violation). The error message identifies the duplicate column(s): `Found duplicate column(s): <duplicateCols>`. ^[delta_duplicate_columns_found-error-condition-databricks-on-aws.md]

## Sub‑Conditions

The error is reported under several sub‑conditions, each indicating the context in which the duplicate was found. The sub‑condition name appears as part of the exception message or stack trace.

| Sub‑condition          | Description                                                                      |
|------------------------|----------------------------------------------------------------------------------|
| `ADDING_COLUMNS`       | The duplicate was found while adding columns.                                    |
| `CLUSTER_BY`           | The duplicate was found in a `CLUSTER BY` clause.                                |
| `CONVERT_TO_DELTA`     | The duplicate was found during conversion to Delta.                              |
| `DATA`                 | The duplicate was found in the data being saved.                                 |
| `EXISTING_SCHEMA`      | The duplicate was found in the existing table schema (or in the metadata update).|
| `PARTITION_COLUMNS`    | The duplicate was found in the partition columns.                                |
| `PARTITION_SCHEMA`     | The duplicate was found in the partition schema.                                 |
| `READ_SCHEMA`          | The duplicate was found in the schema of the data being read.                    |
| `REPLACING_COLUMNS`    | The duplicate was found while replacing columns.                                 |
| `SPECIFIED_COLUMNS`    | The duplicate was found in the specified columns.                                |
| `TABLE_SCHEMA`         | The duplicate was found in the table schema.                                     |

^[delta_duplicate_columns_found-error-condition-databricks-on-aws.md]

## Common Scenarios

Duplicate column errors typically arise when:
- A schema evolution operation (e.g., `ALTER TABLE ADD COLUMNS`) attempts to add a column that already exists.
- A `REPLACE COLUMNS` operation includes a column name more than once.
- The partitioning column list contains duplicates.
- Data being ingested into a Delta table has multiple columns with the same name.
- A conversion from a Parquet or other format to Delta produces a schema with duplicate names.
- A `CLUSTER BY` clause (used in Delta Liquid Clustering) references the same column multiple times.

In each case, Delta Lake rejects the operation to prevent ambiguous schema definitions. ^[delta_duplicate_columns_found-error-condition-databricks-on-aws.md]

## Related Concepts

- [Delta Lake](/concepts/delta-lake.md) – The storage layer that enforces schema constraints.
- Schema Evolution – The broader practice of modifying Delta table schemas over time.
- Delta Table Schema Enforcement
- [SQLSTATE 42711](/concepts/sqlstate-42711.md)

## Sources

- delta_duplicate_columns_found-error-condition-databricks-on-aws.md

# Citations

1. [delta_duplicate_columns_found-error-condition-databricks-on-aws.md](/references/delta_duplicate_columns_found-error-condition-databricks-on-aws-42950ac1.md)
