#1241-operand should contain one column (s)

#1241-operand should contain 1 column (s)
SELECT O. * , (
SELECT COUNT (*)
From Purn_order_product as Op
WHERE Op.op_oordernum = O.o_num
) as OP_CNT, (

SELECT *
From Purn_order_product as Op
INNER JOIN purn_product as P on (p.p_it = Op.op_pcode)
WHERE Op.op_oordernum = O.o_num
ORDER by Op.op_uid ASC
LIMIT 1
) as P_info
From Purn_order as O
ORDER by O_rdate DESC
LIMIT 0, 50

Excuse me,
The above SQL statement prompts an error:
#1241-operand should contain 1 column (s)
How does this work?
Please give me some details.
Thank you
------to solve the idea----------------------
SELECT O. * ,
(SELECT count (*) from Purn_order_product as op WHERE op.op_oordernum = o.o_num) As OP_CNT,
(SELECT *From Purn_order_product as op INNER joins purn_product as P on (p.p_it = Op.op_pcode)
WHERE p.op_oordernum = O.o_num ORDER by op.op_uid ASC LIMIT 1) As P_info
From Purn_order as O
ORDER by O_rdate DESC
LIMIT 0, 50

There's a problem with the set broken place!
You can't assign multiple fields to an alias, which logically doesn't make sense.
That one *Should, and can only be a definite column name

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