How to ADD PRIMARY KEY in Amazon Redshift

How do I add a primary key to a table in Amazon Redshift?

ADD PRIMARY KEY lets you declare one or more columns as the table’s unique identifier, improving query planning and data modeling in Amazon Redshift.

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Description

Why declare a primary key in Redshift?

Primary keys are metadata only—Redshift does not enforce uniqueness—yet they guide the query planner and SVV tables, enabling better join strategies and vacuum operations.

What is the syntax to add a primary key?

Use ALTER TABLE for existing tables or specify the constraint inside CREATE TABLE. Give the constraint a meaningful name for maintainability.

How do I add a primary key while creating a table?

Embed the PRIMARY KEY clause directly after the column list.This approach keeps DDL concise and avoids later metadata changes.

How do I add a primary key to an existing table?

Run ALTER TABLE … ADD CONSTRAINT. Redshift rewrites only system metadata, so the statement is fast even on large tables.

Can I add a composite primary key?

Yes—list multiple columns inside the parentheses.Composite keys are common in join tables like OrderItems.

Best practices for primary keys in Redshift

Pick low-cardinality columns, avoid wide composite keys, and co-locate distribution style with primary key where possible to minimize data movement.

Common mistakes

Declaring a primary key and assuming uniqueness enforcement is the biggest pitfall. Another mistake is forgetting to ANALYZE after bulk loads, which leaves the planner blind.

Why How to ADD PRIMARY KEY in Amazon Redshift is important

How to ADD PRIMARY KEY in Amazon Redshift Example Usage


--Add a primary key to Products table
ALTER TABLE Products
ADD CONSTRAINT pk_products PRIMARY KEY(id);

How to ADD PRIMARY KEY in Amazon Redshift Syntax


--Create table with primary key
a) CREATE TABLE Customers (
       id INT NOT NULL,
       name VARCHAR(100),
       email VARCHAR(100),
       created_at TIMESTAMP,
       CONSTRAINT pk_customers PRIMARY KEY(id)
   );

--Add primary key to an existing table
b) ALTER TABLE Orders
   ADD CONSTRAINT pk_orders PRIMARY KEY(id);

--Composite primary key example
c) ALTER TABLE OrderItems
   ADD CONSTRAINT pk_orderitems PRIMARY KEY(order_id, product_id);

Common Mistakes

Assuming ADD PRIMARY KEY enforces uniqueness. Redshift stores the key only for query planning. Use ETL checks or COPY column encodings to guarantee true uniqueness.
Adding a primary key without running ANALYZE or VACUUM. The planner may still pick sub-optimal plans if statistics are stale. Analyze the table after large inserts.