Data manipulation language (DML) statements

Introduction to BigQuery

Matt Forrest

Field CTO

Overview of data manipulation in BigQuery

INSERT: Add new rows of data.
UPDATE: Modify existing values in a row.
DELETE: Remove unwanted data from a tables.
MERGE: Statement that can combine INSERT, UPDATE, and DELETE statements into one statement.
CREATE TABLE AS: Creates a new table from a query result.

Considerations and performance

Group DML statements together when possible rather than running them individually
You must use a WHERE condition when running an UPDATE statement
Consider using table partitions and clusters

¹ https://cloud.google.com/bigquery/docs/reference/standard-sql/data-manipulation-language

INSERT

Add records to tables

-- Define the columns in the parentheses 
INSERT INTO customers (customer_id, name, email)

-- Each value is a row to be inserted
VALUES (1, "John Doe", "[email protected]"),
(2, "Jane Doe", "[email protected]"),
(3, "Alice Smith", "[email protected]");

UPDATE

Changing data based on a condition

UPDATE customers
-- Set one column for each SET statement
SET email = "[email protected]"
-- Make sure to include where otherwise all
-- rows will be updated
WHERE customer_id = 1;

UPDATE together with subqueries or joins

UPDATE customers c
SET c.email = e.email
FROM emails e
WHERE c.customer_id = 1;

DELETE

DELETE permanently removes records and can't be reversed

DELETE FROM customers

-- Include WHERE to ensure only specific rows are deleted
WHERE customer_id = 3;

DELETE FROM customers c
JOIN emails e USING (customer_id)
WHERE email = '[email protected]'

MERGE

Combines INSERT, UPDATE, and DELETE in a single operation

-- Sets the customers table as the target
MERGE customers AS target

-- The source is set to new_customers
USING new_customers AS source

-- Matching condition
ON target.customer_id = source.customer_id

-- If the emails do not match, update the email
WHEN MATCHED AND target.email != source.email THEN
  UPDATE SET email = source.email

-- If the match is not met, insert the record
WHEN NOT MATCHED THEN
  INSERT (customer_id, name, email) VALUES 
  (source.customer_id, source.name, source.email);

CREATE TABLE

Create new tables from queries

CREATE TABLE active_customers AS
SELECT customer_id, name, email 
FROM customers
WHERE last_active_date > DATE_SUB(CURRENT_DATE(), INTERVAL 30 DAY);

Let's practice!

Introduction to BigQuery