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// 写法一SELECT m.*, s.* FROM manualcase as m INNER JOIN step as s on s.manualcase_id = m.id// 写法二SELECT m.*, s.* FROM manualcase as m JOIN step as s on s.manualcase_id = m.id// 写法三SELECT m.*, s.* FROM manualcase m JOIN step s on s.manualcase_id = m.id
上述三种内连接写法等同于
SELECT * FROM manualcase m, step s WHERE s.manualcase_id = m.id2、左外连接和右外连接 (1)左外连接(外连接与where同时使用)
SELECT m.*, s.* FROM manualcase as m LEFT JOIN step as s on s.manualcase_id = 1021 WHERE m.module_id=100
(2)右外连接
SELECT m.*, s.* FROM step as s RIGHT JOIN manualcase as m on s.manualcase_id = 1021 WHERE m.module_id=100
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