Re: Confused as to why this sql statement is not working

[Barry Galbraith]

Quote

('x-' + B.id)

In SQL '+' is an arithmetic operator meaning 'add'

If you want to concatenate, then you need concat()
https://dev.mysql.com/doc/refman/8.0/en/string-functions.html#function_concat

Also, the order of evaluation of SQL is not quite what you think. The FROM clause is actually evaluated before the SELECT, so CID doesn't exist here

inner join B on A.xid = CID

You'll need to specify the ON condition in terms of a field in A and a field in B

from A 
inner join B on A.xid = B.some_field

Good luck,
Barry.