SELECT a.id, a.name, b.ip FROM tabel1 as a, table2 as b WHERE a.id = 2; a.id是主键, 唯一值, 我这样查询, 返回和数据表一样多条的相同记录 比如, a.id = 3,. 数据有5条记录, 就返回5条这样a.id = 3的记录
SELECT a.id, a.name, b.ip FROM tabel1 as a, table2 as b WHERE a.id = 2; 等价于SELECT a.id, a.name, b.ip FROM tabel1 as a, (select * from table2 WHERE a.id = 2) as b; 就是两个结果集的卡迪尔积,正确的做法应该加上table1和table2的关联关系,如SELECT a.id, a.name, b.ip FROM tabel1 as a, table2 as b WHERE a.id=b.id and a.id = 2;
FROM tabel1 as a, (select * from table2 WHERE a.id = 2) as b; 就是两个结果集的卡迪尔积,正确的做法应该加上table1和table2的关联关系,如SELECT a.id, a.name, b.ip FROM tabel1 as a, table2 as b
WHERE a.id=b.id and a.id = 2;