How to DROP COLUMN in BigQuery

How do I drop a column in BigQuery without losing critical data?

ALTER TABLE … DROP COLUMN permanently removes one or more columns from a BigQuery table.

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Description

What does ALTER TABLE DROP COLUMN do in BigQuery?

ALTER TABLE … DROP COLUMN deletes a column’s definition and its stored data. The change is immediate and cannot be rolled back, so always back up critical data first.

How do I drop a single column?

Run ALTER TABLE dataset.table DROP COLUMN column_name;. BigQuery instantly removes the column from the table schema and underlying storage.

How do I drop multiple columns at once?

Separate the column names with commas. BigQuery executes the operation atomically, so either all specified columns are dropped or none.

What is the exact syntax?

The syntax section below lists every option. Fully qualify the table if you work across multiple projects to avoid accidental changes.

Which permissions are required?

You need the BigQuery Data Owner or BigQuery Data Editor role on the table, or bigquery.tables.update on the dataset.

Best practices before dropping a column?

1) Back up the table with CREATE TABLE new AS SELECT * EXCEPT(column) FROM old;. 2) Verify no views or queries depend on the column. 3) Remove column references from downstream code.

What happens to partitioning or clustering?

BigQuery blocks the command if the column is part of partitioning or clustering. Re-define those settings before dropping such a column.

How to verify the column is gone?

Query INFORMATION_SCHEMA.COLUMNS or run bq show --schema dataset.table to confirm the schema no longer lists the column.

Common mistakes and how to avoid them

Referencing the wrong table: Always include project and dataset names in production. Dropping a needed column: Search code repositories for usages before executing.

Need to undo? Use table versions

If you enabled table snapshots or created a backup table, you can restore the column by recreating the table schema from the backup.

Why How to DROP COLUMN in BigQuery is important

How to DROP COLUMN in BigQuery Example Usage


-- Remove the obsolete "discount_code" column from the ecommerce Orders table
ALTER TABLE `shop.prod.Orders`
DROP COLUMN discount_code;

How to DROP COLUMN in BigQuery Syntax


-- Drop one column
ALTER TABLE `myproj.analytics.Orders`
DROP COLUMN discount_code;

-- Drop multiple columns
ALTER TABLE `myproj.analytics.Orders`
DROP COLUMN discount_code, coupon_applied;

-- Safe approach: create a backup first
CREATE TABLE `myproj.backups.Orders_20240101` AS
SELECT * FROM `myproj.analytics.Orders`;

-- Then drop the column
ALTER TABLE `myproj.analytics.Orders` DROP COLUMN discount_code;

Common Mistakes

Omitting project and dataset: Running ALTER TABLE Orders DROP COLUMN col; in a shared environment may target an unintended default dataset. Always qualify the table as `project.dataset.table`.
Dropping a partition or clustering column: BigQuery rejects the command, but scripts may fail silently. Repartition or recluster the table first, then drop the column.