网站域名怎样选择,手机发布WordPress,网易邮箱163 com登录,国际网站建设在数据库中tableA连接tableB如下#xff1a;tableA:a1 a21 12 23 24 3tableB:b1 b22 12 23 33 46 5笛卡尔积#xff1a;select * from tableA, tableB.1 1 2 11 1 2 21 1 3 31 1 3 41 1 6 52…在数据库中tableA连接tableB如下tableA:a1 a21 12 23 24 3tableB:b1 b22 12 23 33 46 5笛卡尔积select * from tableA, tableB.1 1 2 11 1 2 21 1 3 31 1 3 41 1 6 52 2 2 12 2 2 22 2 3 32 2 3 42 2 6 53 2 2 13 2 2 23 2 3 33 2 3 43 2 6 54 3 2 14 3 2 24 3 3 34 3 3 44 3 6 5内连接select * from tableA a inner join tableB b where a.a2 b.b1.2 2 12 2 23 2 13 2 24 3 34 3 4左外连接select * from tableA a left join tableB b where a.a2 b.b1.1 1 null2 2 12 2 23 2 13 2 24 3 34 3 4右外连接select * from tableA a right join tableB b where a.a2 b.b1.2 2 12 2 23 2 13 2 24 3 34 3 4null 6 5全连接select * from tableA a full join tableB b where a.a2 b.b1.1 1 null2 2 12 2 23 2 13 2 24 3 34 3 4null 6 5
