SQL Server 2019

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CREATE TABLE orders (
  id integer,
  order_comment varchar(30),
  customer_id integer
);
CREATE TABLE customers (
  id integer,
  customer_name varchar(30)
);
INSERT INTO orders VALUES (1,null,1)
INSERT INTO orders VALUES (2,'Test',2)
INSERT INTO orders VALUES (3,'Bert;Test',3)
3 rows affected

INSERT INTO customers VALUES (1,'Frank')
INSERT INTO customers VALUES (2,'Maria')
INSERT INTO customers VALUES (3,'Bert')
3 rows affected

SELECT * FROM orders;


id
order_comment
customer_id


1
null
1

2
Test
2

3
Bert;Test
3


SELECT * FROM customers;


id
customer_name


1
Frank

2
Maria

3
Bert


UPDATE o SET order_comment=CONCAT(c.customer_name,';',o.order_comment)
FROM
orders o
LEFT JOIN customers c ON c.id=o.customer_id
WHERE o.order_comment IS NULL OR o.order_comment NOT LIKE CONCAT(c.customer_name,'%');
2 rows affected

SELECT * FROM orders;


id
order_comment
customer_id


1
Frank;
1

2
Maria;Test
2

3
Bert;Test
3