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Legal Studies統計具有相同年齡的學生的頻率的 MySQL 查詢？
您可以為此使用 COUNT(*) 和 GROUP BY。首先讓我們建立一個表 −
mysql> create table DemoTable ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentAge int ); Query OK, 0 rows affected (0.59 sec)
使用 insert 命令在表中插入記錄 −
mysql> insert into DemoTable(StudentAge) values(16); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable(StudentAge) values(17); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable(StudentAge) values(18); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(StudentAge) values(17); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(StudentAge) values(17); Query OK, 1 row affected (0.23 sec) mysql> insert into DemoTable(StudentAge) values(17); Query OK, 1 row affected (0.08 sec) mysql> insert into DemoTable(StudentAge) values(18); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable(StudentAge) values(18); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable(StudentAge) values(19); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable(StudentAge) values(19); Query OK, 1 row affected (0.07 sec) mysql> insert into DemoTable(StudentAge) values(16); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(StudentAge) values(16); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable(StudentAge) values(15); Query OK, 1 row affected (0.16 sec)
使用 select 語句顯示錶中的所有記錄 −
mysql> select * from DemoTable;
這會產生以下輸出 −
+-----------+------------+ | StudentId | StudentAge | +-----------+------------+ | 1 | 16 | | 2 | 17 | | 3 | 18 | | 4 | 17 | | 5 | 17 | | 6 | 17 | | 7 | 18 | | 8 | 18 | | 9 | 19 | | 10 | 19 | | 11 | 16 | | 12 | 16 | | 13 | 15 | +-----------+------------+ 13 rows in set (0.00 sec)
以下是計數頻率的查詢 −
mysql> select StudentAge,count(*) AS `AgeFrequency` from DemoTable group by StudentAge;
這會產生以下輸出 −
+------------+--------------+ | StudentAge | AgeFrequency | +------------+--------------+ | 16 | 3 | | 17 | 4 | | 18 | 3 | | 19 | 2 | | 15 | 1 | +------------+--------------+ 5 rows in set (0.05 sec)
更新於： 30-Jul-2019
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