Shulou(Shulou.com)06/01 Report--

Table boy, the data are as follows:

Table girl, the data are as follows:

1. Internal connection inner join:

Question: use sql to find out the complete family ID and user name of the family in the boy and girl tables?

Select boy.hid,boy.name,girl.hid,girl.name from boy inner join girl on boy.hid=girl.hid

Second, the left connection left join or the left outer connection left outer join:

Question: use sql to find out the other half of all users in the boy table?

Select boy.hid,boy.name,girl.hid,girl.name from boy left join girl on boy.hid=girl.hid

3. Connect right join on the right or right outer join on the outside:

Question: use sql to find out the other half of all users in the girl table?

Select boy.hid,boy.name,girl.hid,girl.name from boy right join girl on boy.hid=girl.hid

4. Complete external connection full join or full outer join:

The full outer join returns all rows in the left and right tables. When a row does not match a row in another table, the select list column of the other table contains null values.

Note: mysql does not support it, oracle supports it.

Select boy.hid,boy.name,girl.hid,girl.name from boy full join girl on boy.hid=girl.hid

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.