MySQL 8.0

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create table a_test_company (
companyID int ,
companyName varchar(25));

insert into a_test_company values 
(1,'companyA'),
(2,'companyB'),
(3,'companyC'),
(4,'companyD');


create table a_test_contact (
contactID int,
contactName varchar(25),
companyName varchar(25),
companyID int );

insert into a_test_contact values 
(1,'contactA','companyA',NULL),
(2,'contactB','companyA',NULL),
(3,'contactC','companyB',NULL),
(4,'contactD','companyC',NULL),
(5,'contactE','companyC',NULL);

Records: 4  Duplicates: 0  Warnings: 0



Records: 5  Duplicates: 0  Warnings: 0


select * from a_test_company;
select * from a_test_contact;


companyID
companyName


1
companyA

2
companyB

3
companyC

4
companyD




contactID
contactName
companyName
companyID


1
contactA
companyA
null

2
contactB
companyA
null

3
contactC
companyB
null

4
contactD
companyC
null

5
contactE
companyC
null


update a_test_contact cont 
inner join a_test_company com on cont.companyName=com.companyName
set cont.companyID=com.companyID;

Rows matched: 5  Changed: 5  Warnings: 0


 select * from a_test_contact;;


contactID
contactName
companyName
companyID


1
contactA
companyA
1

2
contactB
companyA
1

3
contactC
companyB
2

4
contactD
companyC
3

5
contactE
companyC
3

contactID	contactName	companyName	companyID
1	contactA	companyA	null
2	contactB	companyA	null
3	contactC	companyB	null
4	contactD	companyC	null
5	contactE	companyC	null