How to use Update Statement in SQL

Once there's data in the table, we might find that there is a need to modify the data. To do so, we can use the UPDATE command. 

The syntax for this is

UPDATE "table_name"
SET "column_1" = [new value]
WHERE {condition}

Example  (1)

say we currently have a table as below:

Table Store_Information

store_name	Sales	Date
Los Angeles	$1500	Jan-05-1999
San Diego	$250	Jan-07-1999
Los Angeles	$300	Jan-08-1999
Boston	$700	Jan-08-1999

and we notice that the sales for Los Angeles on 01/08/1999 is actually $500 instead of $300, and that particular entry needs to be updated. To do so, we use the following SQL query:

UPDATE Store_Information
SET Sales = 500
WHERE store_name = "Los Angeles"
AND Date = "Jan-08-1999"

The resulting table would look like

Table Store_Information

store_name	Sales	Date
Los Angeles	$1500	Jan-05-1999
San Diego	$250	Jan-07-1999
Los Angeles	$500	Jan-08-1999
Boston	$700	Jan-08-1999

In this case, there is only one row that satisfies the condition in the WHERE clause. If there are multiple rows that satisfy the condition, all of them will be modified. If no WHERE clause is specified, all rows will be modified.

It is also possible to UPDATE multiple columns at the same time. The syntax in this case would look like the following:

UPDATE "table_name"SET column_1 = [value1], column_2 = [value2]

WHERE {condition}

Example #2 - Simple example:

Let's take a look at a very simple example.

UPDATE suppliers
SET name = 'HP'
WHERE name = 'IBM';

This statement would update all supplier names in the suppliers table from IBM to HP.

Example #3 - Updating multiple columns example:

Let's take a look at an example where you might want to update more than one column with a single UPDATE statement.

UPDATE suppliers
SET name = 'Apple', product = 'iPhone'
WHERE name = 'Rim';

When you wish to update multiple columns, you can do this by separating the column/value pairs with commas.

This statement would update the supplier name to "Apple" and product to "iPhone" where the name of the supplier is "Rim".

Example #4 - More complex example:

You can also perform more complicated updates.

You may wish to update records in one table based on values in another table. Since you can't list more than one table in the UPDATE statement, you can use the EXISTS clause.

For example:

UPDATE suppliers
SET supplier_name =	( SELECT customers.name FROM customers WHERE customers.customer_id = suppliers.supplier_id)
WHERE EXISTS   ( SELECT customers.name     FROM customers     WHERE customers.customer_id = suppliers.supplier_id);

Whenever a supplier_id matched a customer_id value, the supplier_name would be overwritten to the customer name from the customers table.

Learn more about the EXISTS condition.

Practice Exercise #1:

Based on the suppliers table populated with the following data, update the city to "Santa Clara" for all records whose supplier_name is "NVIDIA".

CREATE TABLE suppliers
(	supplier_id	number(10)	not null,
	supplier_name	varchar2(50)	not null,
	city	varchar2(50),
	CONSTRAINT suppliers_pk PRIMARY KEY (supplier_id)
);

INSERT INTO suppliers (supplier_id, supplier_name, city)
VALUES (5001, 'Microsoft', 'New York');
INSERT INTO suppliers (supplier_id, supplier_name, city)
VALUES (5002, 'IBM', 'Chicago');
INSERT INTO suppliers (supplier_id, supplier_name, city)
VALUES (5003, 'Red Hat', 'Detroit');
INSERT INTO suppliers (supplier_id, supplier_name, city)
VALUES (5004, 'NVIDIA', 'New York');

Solution:

The following SQL statement would perform this update.

UPDATE suppliers
SET city = 'Santa Clara'
WHERE supplier_name = 'NVIDIA';

The suppliers table would now look like this:

SUPPLIER_ID	SUPPLIER_NAME	CITY
5001	Microsoft	New York
5002	IBM	Chicago
5003	Red Hat	Detroit
5004	NVIDIA	Santa Clara

Practice Exercise #2:

Based on the suppliers and customers table populated with the following data, update the city in the suppliers table with the city in the customers table when the supplier_name in the suppliers table matches the customer_name in the customers table.

CREATE TABLE suppliers
(	supplier_id	number(10)	not null,
	supplier_name	varchar2(50)	not null,
	city	varchar2(50),
	CONSTRAINT suppliers_pk PRIMARY KEY (supplier_id)
);

INSERT INTO suppliers (supplier_id, supplier_name, city)
VALUES (5001, 'Microsoft', 'New York');
INSERT INTO suppliers (supplier_id, supplier_name, city)
VALUES (5002, 'IBM', 'Chicago');
INSERT INTO suppliers (supplier_id, supplier_name, city)
VALUES (5003, 'Red Hat', 'Detroit');
INSERT INTO suppliers (supplier_id, supplier_name, city)
VALUES (5005, 'NVIDIA', 'LA');

CREATE TABLE customers
(	customer_id	number(10)	not null,
	customer_name	varchar2(50)	not null,
	city	varchar2(50),
	CONSTRAINT customers_pk PRIMARY KEY (customer_id)
);

INSERT INTO customers (customer_id, customer_name, city)
VALUES (7001, 'Microsoft', 'San Francisco');
INSERT INTO customers (customer_id, customer_name, city)
VALUES (7002, 'IBM', 'Toronto');
INSERT INTO customers (customer_id, customer_name, city)
VALUES (7003, 'Red Hat', 'Newark');

Solution:

The following SQL statement would perform this update.

UPDATE suppliers
SET city =	( SELECT customers.city FROM customers WHERE customers.customer_name = suppliers.supplier_name)
WHERE EXISTS   ( SELECT customers.city     FROM customers     WHERE customers.customer_name = suppliers.supplier_name);

The suppliers table would now look like this:

SUPPLIER_ID	SUPPLIER_NAME	CITY
5001	Microsoft	San Francisco
5002	IBM	Toronto
5003	Red Hat	Newark
5004	NVIDIA	LA