pb clause select

bonjour,
j'ai une requête a effectuer mais je ne parviens toujours pas à resoudre le problème...

mes tables:
sales_order(ORDER_ID ,ORDER_DATE,CUSTOMER_ID,TOTAL)
customer(CUSTOMER_ID,CREDIT_LIMIT)

voici ma requête:

Code:

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select distinct c.name as "name", (select s.total from sales_order s where s.customer_id=c.customer_id and to_char(s.order_date, 'Q')=1) as "1st", (select s.total from sales_order s where s.customer_id=c.customer_id and to_char(s.order_date, 'Q')=2) as "2nd", (select s.total from sales_order s where s.customer_id=c.customer_id and to_char(s.order_date, 'Q')=3) as "3rd", (select s.total from sales_order s where s.customer_id=c.customer_id and to_char(s.order_date, 'Q')=4) as "4th" from customer c, sales_order s where c.customer_id=s.customer_id;

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erreur:
ORA-01427: single-row subquery returns more than one row

Code:

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select distinct c.name as "name", (select sum(s.total) from sales_order s where s.customer_id=c.customer_id and to_char(s.order_date, 'Q')=1 ) as "1st", (select sum(s.total) from sales_order s where s.customer_id=c.customer_id and to_char(s.order_date, 'Q')=2) as "2nd", ... from customer c, sales_order s where c.customer_id=s.customer_id;

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