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我有两组sql查询。两者都为我产生了期望的结果,但我不确定哪一个是有效的以及如何。有人可以向我解释吗?两个sql查询之间的区别(使用连接和不连接)
查询1:
SELECT
od.id, od.order_id, c.firstname, od.category, od.quantity,
od.price, o.order_date, u.username
FROM
orders o inner join order_detail od on o.id=od.order_id
join customer c on c.customerid = o.customer_id
join users u on u.userid = o.issued_by;
问题2:
SELECT
od.id, od.order_id, c.firstname, od.category, od.quantity,
od.price, o.order_date, u.username
FROM
order_detail od, customer c, orders o,
users u WHERE o.id = od.order_id
AND o.customer_id = c.customerid
AND u.userid = o.issued_by;