第一道:
id impl(展示) click(点击)
1 1 1
1 0 1
1 0 0
1 1 0
2 1 0
。。。。
求:每个用户的展示和点击数(正常的) , 每个用户的不正常的展示和点击数
答:(不正常的是:没展示,就点击了)
第二道:
sql中的left join 和 join
准备数据:
a表
+------+------+
| id | name |
+------+------+
| 3 | ccc |
| 2 | bbb |
| 1 | aaa |
+------+------+
b表:
+------+------+
| id | name |
+------+------+
| 1 | aaa |
| 2 | bbb |
| 4 | ccc |
+------+------+
join操作:
mysql> select * from a join b on a.id=b.id;
+------+------+------+------+
| id | name | id | name |
+------+------+------+------+
| 1 | aaa | 1 | aaa |
| 2 | bbb | 2 | bbb |
+------+------+------+------+
left join操作:
mysql> select * from a left join b on a.id=b.id;
+------+------+------+------+
| id | name | id | name |
+------+------+------+------+
| 3 | ccc | NULL | NULL |
| 2 | bbb | 2 | bbb |
| 1 | aaa | 1 | aaa |
+------+------+------+------+