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MySQL之聚合函数
1.AVG()
用法：求平均值
举例：
mysql> select * from t1;+----+------+----------+---------+-------+-------+| id | name | password | test001 | test3 | test4 |+----+------+----------+---------+-------+-------+| 2 | 1 | 1 | 1 | 1 | 1 || 3 | 3 | 4 | 5 | 6 | 7 || 4 | 3 | 4 | 5 | 6 | 7 || 5 | 3 | 4 | 5 | 6 | 7 || 6 | 3 | 4 | 5 | 6 | 7 || 7 | 3 | 4 | 5 | 6 | 7 || 8 | 3 | 4 | 5 | 6 | 7 || 9 | 3 | 4 | 5 | 6 | 7 || 10 | 3 | 4 | 5 | 6 | 7 |+----+------+----------+---------+-------+-------+9 rows in set (0.00 sec)mysql> select AVG(id) from t1;+---------+| AVG(id) |+---------+| 6.0000 |+---------+1 row in set (0.00 sec)
2.COUNT()
用法：记录的条数
举例：
mysql> select COUNT(id) from t1;+-----------+| COUNT(id) |+-----------+| 9 |+-----------+1 row in set (0.00 sec)
3.MAX()
用法：返回最大值
举例：
mysql> select MAX(id) from t1;+---------+| MAX(id) |+---------+| 10 |+---------+1 row in set (0.01 sec)
4.MIN()
用法：返回最小值
举例：
mysql> select MIN(id) from t1;+---------+| MIN(id) |+---------+| 2 |+---------+1 row in set (0.00 sec)
5.SUM()
用法：求和
举例：
mysql> select SUM(id) from t1;+---------+| SUM(id) |+---------+| 54 |+---------+1 row in set (0.00 sec)
其他：MD5(),PASSWORD()
mysql> select MD5(‘MYSQL‘);+----------------------------------+| MD5(‘MYSQL‘) |+----------------------------------+| 14498b83dd1667a0c78f4fdaf5afbf4b |+----------------------------------+1 row in set (0.00 sec)mysql> select PASSWORD(‘MYSQL‘);+-------------------------------------------+| PASSWORD(‘MYSQL‘) |+-------------------------------------------+| *A97AF8E14502C1B988202FB7B96CF565B6523F9D |+-------------------------------------------+1 row in set (0.00 sec)mysql> select ENCYPT(‘MYSQL‘);ERROR 1305 (42000): FUNCTION test.ENCYPT does not existmysql> select ENCRYPT(‘MYSQL‘);+------------------+| ENCRYPT(‘MYSQL‘) |+------------------+| NULL |+------------------+1 row in set (0.03 sec)
MySQL之聚合函数
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