How to ADD COLUMN in BigQuery

Galaxy Glossary

How do I add a new column to an existing BigQuery table?

ALTER TABLE … ADD COLUMN inserts one or more new columns into an existing BigQuery table without rewriting the whole table.

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Description

What does ALTER TABLE ADD COLUMN do?

It appends new fields to an existing BigQuery table, preserving all current data and schema. No data rewrite or downtime occurs, so the table stays query-able.

How do I add a single column?

Use ALTER TABLE dataset.table ADD COLUMN column_name data_type. Include IF NOT EXISTS to avoid errors when the column is already there.

Example: Add phone to Customers

ALTER TABLE ecommerce.Customers ADD COLUMN IF NOT EXISTS phone STRING;

Can I add multiple columns at once?

Yes—separate definitions with commas.

ALTER TABLE ecommerce.Products ADD COLUMN IF NOT EXISTS color STRING, ADD COLUMN IF NOT EXISTS weight FLOAT64;

How do I set default values or constraints?

BigQuery lets you add column options such as DEFAULT expressions and NOT NULL constraints in the same statement.

ALTER TABLE ecommerce.Orders ADD COLUMN IF NOT EXISTS status STRING DEFAULT 'pending' NOT NULL;

Does adding a column lock the table?

No locks are taken; queries and inserts continue to run. The new column shows NULL (or its DEFAULT) for existing rows.

Best practices for ecommerce databases

Use IF NOT EXISTS in migrations, add DEFAULT for new NOT NULL fields, and version-control schema changes alongside application code.

What happens to existing data?

Existing rows receive NULL or the specified DEFAULT. No backfill occurs unless you run an UPDATE after the schema change.

Why How to ADD COLUMN in BigQuery is important

How to ADD COLUMN in BigQuery Example Usage


-- Add a discount_code column to Orders with a default
ALTER TABLE ecommerce.Orders
ADD COLUMN IF NOT EXISTS discount_code STRING DEFAULT '';

-- Verify the change
SELECT discount_code FROM ecommerce.Orders LIMIT 5;

How to ADD COLUMN in BigQuery Syntax


ALTER TABLE [IF EXISTS] `project.dataset.table`
  ADD COLUMN [IF NOT EXISTS] column_name data_type
    [NOT NULL] [DEFAULT (expression)]
    [OPTIONS(option_list)]
[, ADD COLUMN …];

Common Mistakes

Omitting IF NOT EXISTS. Running the statement twice raises the error "Duplicate column name". Fix by adding IF NOT EXISTS or checking INFORMATION_SCHEMA first.
Adding a NOT NULL column without a DEFAULT. BigQuery rejects the change because existing rows would violate the constraint. Supply a DEFAULT or add the column nullable, then backfill and alter to NOT NULL.

Frequently Asked Questions (FAQs)

Can I add a column to a view?

No. ALTER TABLE applies only to physical tables. Update the view definition instead.

How do I add a nested field inside a STRUCT?

Use ALTER TABLE … ADD COLUMN field STRUCT. You cannot add a field directly to an existing STRUCT element.

Is the operation billed?

Schema changes themselves are free. Only subsequent queries that reference the new column incur standard query costs.

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