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在姓氏记录的基础上在MySQL查询中添加列数？

2024-04-24 04:43:15 421

让我们首先创建一个表-

mysql> create table DemoTable
(
   Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   FirstName varchar(100),
   LastName varchar(100)
);

使用插入命令在表中插入一些记录-

mysql> insert into DemoTable(FirstName,LastName) values('David','Miller');
mysql> insert into DemoTable(FirstName,LastName) values('Carol','Miller');
mysql> insert into DemoTable(FirstName,LastName) values('John','Doe');

使用select语句显示表中的所有记录-

mysql> select *from DemoTable;

这将产生以下输出-

+----+-----------+----------+
| Id | FirstName | LastName |
+----+-----------+----------+
|  1 | David     | Miller   |
|  2 | Carol     | Miller   |
|  3 | John      | Doe      |
+----+-----------+----------+
3 rows in set (0.00 sec)

以下是为姓氏记录添加列计数的查询，例如“Miller”出现两次：

mysql> select Id, FirstName, LastName,Count from DemoTable tbl1
   JOIN (select count(*) as Count, LastName from DemoTable GROUP BY LastName) tbl2
   using(LastName);

这将产生以下输出-

+----+-----------+----------+-------+
| Id | FirstName | LastName | Count |
+----+-----------+----------+-------+
|  1 | David     | Miller   |     2 |
|  2 | Carol     | Miller   |     2 |
|  3 | John      | Doe      |     1 |
+----+-----------+----------+-------+
3 rows in set (0.00 sec)

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在姓氏记录的基础上在MySQL查询中添加列数？

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