MySQL - Update column value based on joined table column value - mysql

Question

I've been reading through SO and other sites, and have followed a few examples; however, my SQL statments is still not performing as required.
I have two tables
parts
============================
pmkParts fnkManufacturer
----------------------------
0 Penn-Union
1 Schneider
2 Telemecanique
and
manufacturer
===============================
Manufacturer pmkManufacturer
-------------------------------
Penn-Union 45
Schneider 56
Telemecanique 12
I want to change the parts table into
parts
============================
pmkParts fnkManufacturer
----------------------------
0 45
1 56
2 12
Here is the SQL statement I tried.
Update parts
SET parts.fnkManufacturer = (
SELECT manufacturer.pmkManufacturer
FROM manufacturer
WHERE manufacturer.pmkManufacturer = parts.fnkManufacturer
)
That is changing the correct column, but it is filling it with 'NULLS' rather than the foreign key (manufacturer). I think there should be a join somewhere in there, but I'm not sure where.
Any tips?
----------
EDIT: Answer:
Here is the SQL statement that worked. Thanks MarcB for the help.
Update parts
SET parts.fnkManufacturer = (
SELECT manufacturer.pmkManufacturer
FROM manufacturer
WHERE manufacturer.Manufacturer= parts.fnkManufacturer
)

Answer 1

Try changing your query like below using a update join query. Again, you are joining on the wrong column, you actually should be joining to manufacturer.Manufacturer column rather.
Update parts p
JOIN manufacturer m ON m.Manufacturer = p.fnkManufacturer
SET p.fnkManufacturer = m.pmkManufacturer;

Answer 2

Your pmkManufacturer looks like int so it is better to add new int field to parts, update it and then remove old column. Something like this.
alter table dbo.parts add pmkManufacturer int
update dbo.parts
set pmkManufacturer = m.pmkManufacturer
from dbo.parts p
inner join dbo.Manufacturer m on p.fnkManufacturer = m.manufacturer

Answer 3

The best solution, you could use INNER JOIN, I for example :
update parts p
inner join manufacturer m on
p.pmkManufacturer = m.Manufacturer
set p.pmkManufacturer = m.pmkManufacturer
Howerver, in your case, if I was wrong, you want to update pmkManufacturer while pmkManufacturer is actually the condition ON for INNER JOIN so I'm not sure that it'okay for request. If not, it isn't also difficult, you could add a new column : pmk_bis_manufacturer and set the value into this column, then delete the old column pmkManufacturer and change the name of new column if nescessary.
One tip for you : the name of columns database, I prefer setting :
pmk_manufacturer instead of pmkManufacturer because capital letter in the name
could make one problem in the futur. For example : for ORM Doctrine,
it isn't good :D