Mysql学习mysql统计多表交叉组合总数实例

发布时间：2020-12-12 03:13:49 所属栏目：MySql教程来源：网络整理

导读：《Mysql学习mysql统计多表交叉组合总数实例》要点：本文介绍了Mysql学习mysql统计多表交叉组合总数实例，希望对您有用。如果有疑问，可以联系我们。导读：例子,mysql如何统计多表交叉组合总数.mysql -h localhost -u root -pmysql use world; Database cha

《Mysql学习mysql统计多表交叉组合总数实例》要点：
本文介绍了Mysql学习mysql统计多表交叉组合总数实例，希望对您有用。如果有疑问，可以联系我们。

导读：例子,mysql如何统计多表交叉组合总数. >mysql -h localhost -u root -pmysql> use world; Database changed mysql> show tabl...

MYSQL实例例子,mysql如何统计多表交叉组合总数.
?

MYSQL实例>mysql -h localhost -u root -p?

MYSQL实例mysql> select count(*) from city;?
+----------+?
| count(*) |?
+----------+?
|???? 4079 |?
+----------+?
1 row in set (0.00 sec)?

MYSQL实例mysql> select count(*) from country;?
+----------+?
| count(*) |?
+----------+?
|????? 239 |?
+----------+?
1 row in set (0.00 sec)?

MYSQL实例mysql> select 4079*239?
??? -> ;?
+----------+?
| 4079*239 |?
+----------+?
|?? 974881 |?
+----------+?
1 row in set (0.00 sec)?

MYSQL实例这里就是计算交叉组合数量,因为他们之间一个相同的关联字段
?

mysql> select count(*) from city,country?
??? -> ;?
+----------+?
| count(*) |?
+----------+?
|?? 974881 |?
+----------+?
1 row in set (0.00 sec)?

MYSQL实例实际上mysql所做的操作就是把你所查询表的数量相乘得到的结果!
?

mysql> select count(*) from city,country,countrylanguage;?
+-----------+?
| count(*)? |?
+-----------+?
| 959282904 |?
+-----------+?
1 row in set (0.02 sec)?
?
mysql> select count(*) from countrylanguage;?
+----------+?
| count(*) |?
+----------+?
|????? 984 |?
+----------+?
1 row in set (0.00 sec)?
?
mysql> select 4079*239*984;?
+--------------+?
| 4079*239*984 |?
+--------------+?
|??? 959282904 |?
+--------------+?
1 row in set (0.00 sec)

（编辑：李大同）

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