SELECT * FROM a left join b ON a.bid = b.id LEFT JOIN c ON a.cid=c.id
SELECT * FROM (SELECT * FROM a left joint b ON a.bid = b.id) as t
LEFT JOIN c ON t.cid=c.id
这两个结果不一样吗?
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SELECT * FROM a left join b ON a.bid = b.id LEFT JOIN c ON a.cid=c.id SELECT * FROM (SELECT * FROM a left joint b ON a.bid = b.id) as t LEFT JOIN c ON t.cid=c.id 这两个结果不一样吗?
另外,你也可以显示一下2个语句的执行计划:
explain SELECT * FROM a left join b ON a.bid = b.id LEFT JOIN c ON a.cid=c.id;
explain SELECT * FROM (SELECT * FROM a left joint b ON a.bid = b.id) as t
LEFT JOIN c ON t.cid=c.id;