Node.js - MySQL Order By_Node.js 菜鸟教程

在 Node.js应用程序中，您可能希望按升序或降序从 MySQL 数据库中检索数据。在MySQL中，ORDER BY子句按指定顺序对SELECT语句返回的结果集进行排序。使用 Node.js 应用程序从 MySQL 数据库中检索数据时，mysql 模块中定义的连接对象的 query（）方法的查询字符串参数应具有 ORDER BY 子句。在本章中，通过示例描述了 SELECT 语句中 ORDER BY 子句在 Node.js 应用程序中的各种用例。

SELECT语句中ORDER BY子句的语法如下：

SELECT select_list FROM table_name	
ORDER BY column1 [ASC|DESC], column2 [ASC|DESC], ...;

您可以指定要在 ORDER BY 子句之后进行排序的一列或多列。默认排序顺序为升序（ASC）。

 ORDER BY column1;

若要按降序获取行，请在列名称前面使用 DESC。

 ORDER BY column1 DESC;

数值字段的升序获取字段从最小值到最大值的行数。然而，字符串字段（例如 VARCHAR 或 TEXT）的升序导致从 a 到 z 的字母顺序。同样，对于 DateTime 字段，升序是指按时间顺序排列的顺序，即从较早的日期到较晚的日期。

例

以下Node.js代码，mysql模块的query（）方法按Salas字段的升序返回Employee表中的行。

var mysql = require('mysql');
var con = mysql.createConnection({
	 	host: "localhost",
	 	user: "root",
	 	password: "mypassword",
	 	database: "mydb"
});

var qry =`SELECT * FROM employee ORDER BY salary;`;
con.connect(function (err) {
	 	if (err) throw err;
	 	console.log("Connected!");
	 	con.query(qry, function (err, results) {
	 	 	 if (err) throw err;
	 	 	 console.log(results);
	 	});

	 	con.end();
});

输出

[
	 RowDataPacket { id: 1, name: 'Ravi', age: 25, salary: 25000 },
	 RowDataPacket { id: 3, name: 'Meena', age: 26, salary: 27000 },
	 RowDataPacket { id: 2, name: 'Anil', age: 26, salary: 30000 }
]

作为带有字段的 DESC 关键字的降序示例，将查询字符串更改为以下内容 -

var qry =`SELECT * FROM employee ORDER BY name DESC;`;

结果集将按 employee able 中姓名的降序排列。

[
	 RowDataPacket { id: 1, name: 'Ravi', age: 25, salary: 25000 },
	 RowDataPacket { id: 3, name: 'Meena', age: 26, salary: 27000 },
	 RowDataPacket { id: 2, name: 'Anil', age: 26, salary: 30000 }
]

多列排序

如前所述，您可以在 ORDER BY 子句之后指定一列或多列。这将首先对第一列上的行进行排序。第一列值相同的行按第二列的值排序。实际上，这变成了排序或嵌套排序中的排序。

为了说明多列排序，我们将使用 MySQL 8.0 安装中预装的 world 数据库。世界数据库包括一个城市表，其结构如下：

+-------------+----------+------+-----+---------+----------------+
| Field 	  | Type 	 | Null | Key | Default | Extra 	 	 |
+-------------+----------+------+-----+---------+----------------+
| ID 	 	  | int 	 | NO 	| PRI | NULL 	| auto_increment |
| Name 	 	  | char(35) | NO 	| 	  | 	    | 	 	 	 	 |
| CountryCode | char(3)  | NO 	| MUL | 	    | 	 	 	 	 |
| District 	  | char(20) | NO 	| 	  | 	 	| 	 	 	 	 |
| Population  | int 	 | NO 	| 	  | 0 	 	| 	 	 	 	 |
+-------------+----------+------+-----+---------+----------------+

使用以下Node.js代码，我们将获取按人口升序排序的按地区划分的城市列表。

例

var mysql = require('mysql');
var con = mysql.createConnection({
	 	host: "localhost",
	 	user: "root",
	 	password: "mypassword",
	 	database: "world"
});

var qry =`select * from city where name like 'D%' and countrycode='IND' order by district, population;`;
con.connect(function (err) {
	 	if (err) throw err;
	 	console.log("Connected!");
		
	 	con.query(qry, function (err, results) {
	 	 	 if (err) throw err;
	 	 	 console.log(results);
	 	});

	 	con.end();
});

输出

[
RowDataPacket {
ID: 1276,
Name: 'Dibrugarh',
CountryCode: 'IND',
District: 'Assam',
Population: 120127
},
RowDataPacket {
ID: 1350,
Name: 'Dehri',
CountryCode: 'IND',
District: 'Bihar',
Population: 94526
},
RowDataPacket {
ID: 1138,
Name: 'Darbhanga',
CountryCode: 'IND',
District: 'Bihar',
Population: 218391
},
RowDataPacket {
ID: 1206,
Name: 'Durg',
CountryCode: 'IND',
District: 'Chhatisgarh',
Population: 150645
},
RowDataPacket {
ID: 1351,
Name: 'Delhi Cantonment',
CountryCode: 'IND',
District: 'Delhi',
Population: 94326
},
RowDataPacket {
ID: 1025,
Name: 'Delhi',
CountryCode: 'IND',
District: 'Delhi',
Population: 7206704
},
RowDataPacket {
ID: 1203,
Name: 'Dhanbad',
CountryCode: 'IND',
District: 'Jharkhand',
Population: 151789
},
RowDataPacket {
ID: 1119,
Name: 'Davangere',
CountryCode: 'IND',
District: 'Karnataka',
Population: 266082
},
RowDataPacket {
ID: 1347,
Name: 'Damoh',
CountryCode: 'IND',
District: 'Madhya Pradesh',
Population: 95661
},
RowDataPacket {
ID: 1186,
Name: 'Dewas',
CountryCode: 'IND',
District: 'Madhya Pradesh',
Population: 164364
},
RowDataPacket {
ID: 1113,
Name: 'Dhule (Dhulia)',
CountryCode: 'IND',
District: 'Maharashtra',
Population: 278317
},
RowDataPacket {
ID: 1167,
Name: 'Dindigul',
CountryCode: 'IND',
District: 'Tamil Nadu',
Population: 182477
},
RowDataPacket {
ID: 1117,
Name: 'Dehra Dun',
CountryCode: 'IND',
District: 'Uttaranchal',
Population: 270159
},
RowDataPacket {
ID: 1214,
Name: 'Dabgram',
CountryCode: 'IND',
District: 'West Bengal',
Population: 147217
},
RowDataPacket {
ID: 1082,
Name: 'Durgapur',
CountryCode: 'IND',
District: 'West Bengal',
Population: 425836
}
]

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