What I'm doing here is to add a column (named outOfStock) to my existing table prod_info.

I used this query to generate my outOfStock table.

PHP Code:
SELECT prod_idXSSSplusMLXL FROM prod_info AS outOfStock WHERE
     XS    IS NULL 
&&
     
S     IS NULL &&
     
Splus IS NULL &&
     
M     IS NULL &&
     
L     IS NULL &&
     
XL    IS NULL 
Then I used a LEFT JOIN to combine them.

PHP Code:
SELECT FROM prod_info LEFT JOIN (
  
SELECT prod_idXSSSplusMLXL FROM prod_info AS outOfStock WHERE
     XS    IS NULL 
&&
     
S     IS NULL &&
     
Splus IS NULL &&
     
M     IS NULL &&
     
L     IS NULL &&
     
XL    IS NULL
ON prod_info.prod_id outOfStock.prod_id 
It prompts me this error message:
Every derived table must have its own alias.
I'm totally a goner at subqueries and joins. How does it mean and how do I achieve what I want?

Oh yes, please recommend some really simple reading on joins and subqueries. Most that I'd seen are quite difficult to understand.