SQL - UPDATE JOIN Statement

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The SQL UPDATE JOIN

An UPDATE JOIN in SQL is used to update records in one table based on matching values from another table. By combining the UPDATE statement with a JOIN, you can modify rows in a target table using data from related tables.

This is useful when you need to synchronize or adjust data across multiple tables that share a common key.

Syntax

Following is the basic syntax of the SQL UPDATE JOIN statement:

UPDATE table1
JOIN table2 ON table1.common_field = table2.common_field
SET table1.column_to_update = table2.column_value
WHERE table2.some_column = 'value';

Where, JOIN can be: Regular Join, Natural Join, Inner Join, Outer Join, Left Join, Right Join, Full Join etc.

Example

Assume we have created a table named CUSTOMERS, which contains the personal details of customers including their name, age, address and salary etc., using the following query:

CREATE TABLE CUSTOMERS (
   ID INT NOT NULL,
   NAME VARCHAR (20) NOT NULL,
   AGE INT NOT NULL,
   ADDRESS CHAR (25),
   SALARY DECIMAL (18, 2),       
   PRIMARY KEY (ID)
);

Now, insert values into this table using the INSERT statement as follows:

INSERT INTO CUSTOMERS VALUES
(1, 'Ramesh', 32, 'Ahmedabad', 2000.00 ),
(2, 'Khilan', 25, 'Delhi', 1500.00 ),
(3, 'Kaushik', 23, 'Kota', 2000.00 ),
(4, 'Chaitali', 25, 'Mumbai', 6500.00 ),
(5, 'Hardik', 27, 'Bhopal', 8500.00 ),
(6, 'Komal', 22, 'Hyderabad', 4500.00 ),
(7, 'Muffy', 24, 'Indore', 10000.00 );

The table will be created as:

Let us create another table ORDERS, containing the details of orders made and the date they are made on.

CREATE TABLE ORDERS (
   OID INT NOT NULL,
   DATE VARCHAR (20) NOT NULL,
   CUSTOMER_ID INT NOT NULL,
   AMOUNT DECIMAL (18, 2)
);

Using the INSERT statement, insert values into this table as follows:

INSERT INTO ORDERS VALUES 
(102, '2009-10-08 00:00:00', 3, 3000.00),
(100, '2009-10-08 00:00:00', 3, 1500.00),
(101, '2009-11-20 00:00:00', 2, 1560.00),
(103, '2008-05-20 00:00:00', 4, 2060.00);

The table is displayed as follows:

Following UPDATE JOIN query increments the salary of customers by 1000 with respect to the inflation of their order amount by 500:

UPDATE CUSTOMERS 
JOIN ORDERS 
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID 
SET CUSTOMERS.SALARY = CUSTOMERS.SALARY + 1000, 
ORDERS.AMOUNT = ORDERS.AMOUNT + 500;

We get the following output:

Query OK, 7 rows affected (0.04 sec)
Rows matched: 7  Changed: 7  Warnings: 0

Verification

We can verify whether the changes are reflected in a table by retrieving its contents using the SELECT statement as follows:

SELECT * FROM CUSTOMERS;

The updated CUSTOMERS table is displayed as follows:

Now, check whether the ORDERS table is updated using the following SELECT statement:

SELECT * FROM ORDERS;

The updated ORDERS table is displayed as follows:

UPDATE JOIN with WHERE Clause

An UPDATE JOIN can be combined with a WHERE clause to update only those rows that meet specific conditions after the join. The join defines the relationship between the tables, while the WHERE clause filters which rows should be updated.

Syntax

The syntax of SQL UPDATE JOIN with WHERE clause in MySQL database is as follows:

UPDATE table(s)
JOIN table2 ON column3 = column4
SET table1.column1 = value1, table1.column2 = value2, ...
WHERE condition;

Example

Now, let us execute the following query to increase the salary of customer whose id is 3:

UPDATE CUSTOMERS 
LEFT JOIN ORDERS 
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID 
SET CUSTOMERS.SALARY = CUSTOMERS.SALARY + 1000 
WHERE ORDERS.CUSTOMER_ID = 3;

We get the following output:

Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

Verification

We can verify whether the changes are reflected in a table by retrieving its contents using the SELECT statement as follows.

SELECT * FROM CUSTOMERS;

As we can see in the table below, SALARY value of "Kaushik" is increased by 1000:

The UPDATE JOIN Clause in SQL Server

The SQL UPDATE JOIN clause also works in SQL Server database. But, the syntax of the query is slightly different from that of MySQL. However, the working of it is exactly the same as MySQL query.

In MySQL, the UPDATE statement is followed by the JOIN clause and SET statements respectively. Whereas, in MS SQL Server the SET statement is followed by the JOIN clause.

Syntax

Following is the syntax of the UPDATE JOIN in SQL Server:

UPDATE table1
SET table1.col = table2.col
FROM table1
JOIN table2 ON table1.common_field = table2.common_field
WHERE table2.some_column = 'value';

Example

In this example, we will update values of the CUSTOMERS and ORDERS table that we created above using the following UPDATE JOIN query:

UPDATE CUSTOMERS
SET SALARY = SALARY + 1000
FROM CUSTOMERS 
JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;

We get the output as shown below:

(3 rows affected)

Verification

We can verify whether the changes are reflected in a table by retrieving its contents using the SELECT statement as follows.

SELECT * FROM CUSTOMERS;

The updated CUSTOMERS table is displayed as follows:

SQL UPDATE JOIN Using LEFT JOIN

The LEFT JOIN in an UPDATE statement is used when you want to update records in one table based on matching records from another table, while still considering rows from the left (first) table that do not have a match in the right (second) table.

This is useful when you want to update all rows in the left table regardless of whether they have corresponding rows in the right table.

Syntax

The syntax of SQL UPDATE JOIN using LEFT JOIN is as follows:

UPDATE table1
LEFT JOIN table2 ON table1.common_field = table2.common_field
SET table1.column_to_update = table2.column_value
WHERE condition;

Example

Suppose we want to update the SALARY of all customers by 500 if they have placed an order, otherwise leave their salary unchanged:

UPDATE CUSTOMERS
LEFT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
SET CUSTOMERS.SALARY = CUSTOMERS.SALARY + 500
WHERE ORDERS.CUSTOMER_ID IS NOT NULL;

This ensures that only customers with orders receive the salary increment. We get the output as shown below:

Query OK, 3 rows affected (0.04 sec)
Rows matched: 3  Changed: 3  Warnings: 0

Verification

We can verify the changes by executing the following SELECT query:

SELECT * FROM CUSTOMERS;

You will see that the salary values of customers who placed orders are updated accordingly.

SQL UPDATE JOIN Using INNER JOIN

An INNER JOIN in an UPDATE statement only updates rows in the target table that have matching rows in the joined table. If no match is found, no update occurs for that row.

This is the most common type of UPDATE JOIN when you only want to update related data.

Syntax

The syntax of SQL UPDATE JOIN using INNER JOIN is as follows:

UPDATE table1
INNER JOIN table2 ON table1.common_field = table2.common_field
SET table1.column_to_update = table2.column_value
WHERE condition;

Example

Let us increase the SALARY of only those customers who have placed an order worth more than 2000:

UPDATE CUSTOMERS
INNER JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
SET CUSTOMERS.SALARY = CUSTOMERS.SALARY + 1000
WHERE ORDERS.AMOUNT > 2000;

We get the output as follows:

Query OK, 2 rows affected (0.02 sec)
Rows matched: 2  Changed: 2  Warnings: 0

Verification

We can verify the result by executing the following SELECT query:

SELECT * FROM CUSTOMERS;

Only customers with orders greater than 2000 will have their salaries updated:

Important Points About SQL UPDATE JOIN

Following are some important points you should know for using UPDATE JOIN in SQL:

• Running an UPDATE JOIN without a WHERE clause may update a large number of rows unintentionally.
• Always test your JOIN conditions using a SELECT query before running the UPDATE to ensure the correct rows are targeted.
• In some databases (like MySQL), you can update columns in both tables involved in the join, but in others (like SQL Server), you may only update one table at a time.
• UPDATE JOIN queries can be heavy on performance for large tables. Make sure proper indexes exist on the join columns.
• Use INNER JOIN when you only want to update matching rows. Use LEFT JOIN when you also want to consider rows without matches in the right table.