mysql统计多表交叉组合总数
>mysql -h localhost -u root -p
mysql> use world;Database changedmysql> show tables;+-----------------+| Tables_in_world |+-----------------+| city || country || countrylanguage |+-----------------+3 rows in set (0.00 sec)
mysql> select count(*) from city;+----------+| count(*) |+----------+| 4079 |+----------+1 row in set (0.00 sec)
mysql> select count(*) from country;+----------+| count(*) |+----------+| 239 |+----------+1 row in set (0.00 sec)
mysql> select 4079*239 -> ;+----------+| 4079*239 |+----------+| 974881 |+----------+1 row in set (0.00 sec)
mysql> select count(*) from city,country -> ;+----------+| count(*) |+----------+| 974881 |+----------+1 row in set (0.00 sec)
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)
