Question

hopefully there is a simple resolution to my challenge.

I have a parent table I will call table ‘A’ and a child table called table ‘B’. I would
like to get information from the most recent row in table ‘B’ for a given row in table
‘A’.

For example… parent 12345 in Table ‘A’ has three child rows in table ‘B’. Row number
3 is the most recent row in table ‘B’ for parent 12345. I would like to get row 3’s
information.

I tried quite a few different approaches and could not get it to do what is needed, hence my posting this here.

Thank you in advance.

Answer 1

Use an INNER JOIN on the two tables, relating them by the child id to the parent’s child id:

SELECT b.*
FROM Table_B b INNER JOIN Table_A a
ON b.id = a.Table_B_id 
WHERE a.id = 42
ORDER BY b.id DESC
LIMIT 1

I was going to suggest:

SELECT * FROM Table_B WHERE id IN (
    SELECT Table_B_id FROM Table_A ORDER BY id DESC LIMIT 1
)

But apparently MySQL doesn’t support LIMIT on an inner select.