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法律在 MySQL 中获得不同值并对其进行计数
要获得不同值并对它们进行计数，可以使用 GROUP BY 子句。
语法如下
select yourColumnName,count(*) as anyAliasName from yourTableName group by yourColumnName;
为了理解以上语法，我们创建一个表格。创建表格的查询如下
mysql> create table GroupByAndCountDemo -> ( -> ClientId int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> ClientName varchar(100) -> ); Query OK, 0 rows affected (0.64 sec)
使用 insert 命令在表格中插入一些记录。查询如下
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
Query OK, 1 row affected (0.18 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('Carol');
Query OK, 1 row affected (0.14 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('Sam');
Query OK, 1 row affected (0.15 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('Sam');
Query OK, 1 row affected (0.16 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
Query OK, 1 row affected (0.51 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
Query OK, 1 row affected (0.15 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
Query OK, 1 row affected (0.13 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('Sam');
Query OK, 1 row affected (0.08 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('Sam');
Query OK, 1 row affected (0.47 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('Sam');
Query OK, 1 row affected (0.09 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
Query OK, 1 row affected (0.13 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
Query OK, 1 row affected (0.18 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
Query OK, 1 row affected (0.10 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('David');
Query OK, 1 row affected (0.12 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('Maxwell');
Query OK, 1 row affected (0.17 sec)
mysql> insert into GroupByAndCountDemo(ClientName) values('Maxwell');
Query OK, 1 row affected (0.15 sec)使用 select 语句从表格中显示所有记录。查询如下
mysql> select *from GroupByAndCountDemo;
输出如下
+----------+------------+ | ClientId | ClientName | +----------+------------+ | 1 | John | | 2 | Carol | | 3 | Sam | | 4 | Sam | | 5 | John | | 6 | John | | 7 | John | | 8 | Sam | | 9 | Sam | | 10 | Sam | | 11 | John | | 12 | John | | 13 | John | | 14 | David | | 15 | Maxwell | | 16 | Maxwell | +----------+------------+ 16 rows in set (0.00 sec)
现在让我们使用以下查询获得不同值并对它们进行计数
mysql> select ClientName,count(*) as TotalCount from GroupByAndCountDemo group by ClientName;
以下为输出
+------------+------------+ | ClientName | TotalCount | +------------+------------+ | John | 7 | | Carol | 1 | | Sam | 5 | | David | 1 | | Maxwell | 2 | +------------+------------+ 5 rows in set (0.00 sec)
更新于：2019 年 7 月 30 日
440 次浏览
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