How to use Table output from stored MYSQL Procedure

This can't be done, directly, because the output of an unbounded select in a stored procedure is a result set sent to the client, but not technically a table.

The workaround is to let the proc put the data in a temporary table after creating the table for you. This table will be available only to your connection when the procedure finishes. It will not cause a conflict if somebody else runs the proc at the same time and won't be visible to any other connection.

Add this to the procedure:

DROP TEMPORARY TABLE IF EXISTS foo;
CREATE TEMPORARY TABLE foo SELECT ... your existing select query here ...;

When your procedure finishes, SELECT * FROM foo; will give you what you what you would have gotten from the proc. You can join to it pretty much like any table.

When you're done, drop it, or it will go away on its own when you disconnect. If you run the proc again, it will be dropped and recreated.

Here's a concrete example in MySql 8, based on @Michael-sqlbot's suggestion:

-- Create some test data
drop table if exists someData ;
create table someData (itemId int, itemName varcharacter(20), itemQty int, itemCat int) ;
insert into someData values
(1,'First', 9, 1)
,(2,'Second',50, 3)
,(3,'Third', 12, 5)
,(4,'Fourth', 7, 3)
,(5,'Fifth', 1, 2)
,(6,'Sixth', 1, 1)
,(7,'Seventh', 9, 3)
,(8,'Eighth', 0, 2)
;

-- Just checking that it's all there!
select * from someData ;

-- Define the proc
delimiter //
drop procedure if exists prcSomeData //
create procedure prcSomeData()
    comment 'Create a temporary table called "tmpSomeData"'
begin
    drop table if exists tmpSomeData ;
    create temporary table tmpSomeData as
        select itemCat
            , sum(itemQty) as 'itemsTot'
            , min(itemQty) as 'lowestQty'
            , max(itemQty) as 'highestQty'
            from someData
            group by itemCat
            order by itemCat
        ;
end //
delimiter ;

-- Gotta run the proc to instantiate the temp table
call prcSomeData() ;        -- produces a temporary table "tmpSomeData", exists for the session
-- Now it's usable
select * from tmpSomedata ;

Which produces:

itemCat|itemsTot|lowestQty|highestQty|
-------|--------|---------|----------|
      1|      10|        1|         9|
      2|       1|        0|         1|
      3|      66|        7|        50|
      5|      12|       12|        12|