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Mysql學習mysql統計多表交叉組合總數實例

作者：VEPHP   時間 2017-09-27

《Mysql學習mysql統計多表交叉組合總數實例》要點：
本文介紹了Mysql學習mysql統計多表交叉組合總數實例，希望對您有用。如果有疑問，可以聯系我們。

導讀：例子,mysql如何統計多表交叉組合總數. >mysql -h localhost -u root -pmysql> use world; Database changed mysql> show tabl...

MYSQL實例例子,mysql如何統計多表交叉組合總數.
?

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

MYSQL實例mysql> use world;?
Database changed?
mysql> show tables;?
+-----------------+?
| Tables_in_world |?
+-----------------+?
| city??????????? |?
| country???????? |?
| countrylanguage |?
+-----------------+?
3 rows in set (0.00 sec)?

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

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

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

MYSQL實例這里就是計算交叉組合數量,因為他們之間一個相同的關聯字段
?

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

MYSQL實例實際上mysql所做的操作就是把你所查詢表的數量相乘得到的結果!
?

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)

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