MySQL - 主键

要在JavaScript程序中为字段应用主键，我们需要使用mysql2库的query()函数执行包含PRIMARY KEY关键字的CREATE查询，如下所示：

sql = `CREATE TABLE customers(cust_ID INT NOT NULL primary key, cust_Name VARCHAR(30))`;
con.query(sql);  

要在Java程序中为字段应用主键，我们需要使用JDBC函数execute()执行包含PRIMARY KEY关键字的CREATE查询，如下所示：

String sql = "CREATE TABLE customers(cust_ID INT NOT NULL UNIQUE, cust_Name VARCHAR(30), cust_login_ID INT AUTO_INCREMENT PRIMARY KEY)";
statement.execute(sql);

要在Python程序中为字段应用主键，我们需要使用MySQL Connector/Python的execute()函数执行包含PRIMARY KEY关键字的CREATE查询，如下所示：

primary_key_query = 'CREATE TABLE TEST (ID INT NOT NULL, NAME VARCHAR (20) NOT NULL, AGE INT NOT NULL, PRIMARY KEY (ID))'
cursorObj.execute(primary_key_query)

var mysql = require("mysql2");
var con = mysql.createConnection({
  host: "localhost",
  user: "root",
  password: "password",
}); //Connecting to MySQL

con.connect(function (err) {
  if (err) throw err;
  //   console.log("Connected successfully...!");
  //   console.log("--------------------------");
  sql = "USE TUTORIALS";
  con.query(sql);

  //create a table that stored primary key
  sql = `CREATE TABLE customers(cust_ID INT NOT NULL primary key, cust_Name VARCHAR(30))`;
  con.query(sql);

  //describe table details
  sql = "DESCRIBE TABLE customers";
  con.query(sql, function (err, result) {
    if (err) throw err;
    console.log(result);
  });
});    

输出

生成的输出如下：

[
    {
      id: 1,
      select_type: 'SIMPLE',
      table: 'customers',
      partitions: null,
      type: 'ALL',
      possible_keys: null,
      key: null,
      key_len: null,
      ref: null,
      rows: 1,
      filtered: 100,
      Extra: null
    }
]  

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class PrimaryKey {
   public static void main(String[] args) {
      String url = "jdbc:mysql://localhost:3306/TUTORIALS";
      String username = "root";
      String password = "password";
      try {
         Class.forName("com.mysql.cj.jdbc.Driver");
         Connection connection = DriverManager.getConnection(url, username, password);
         Statement statement = connection.createStatement();
         System.out.println("Connected successfully...!");

         //Create a primary key in the customer table...!;
         String sql = "CREATE TABLE customers(cust_ID INT NOT NULL UNIQUE, cust_Name VARCHAR(30), cust_login_ID INT AUTO_INCREMENT PRIMARY KEY)";
         statement.execute(sql);
         System.out.println("Primary key created successfully...!");
         ResultSet resultSet = statement.executeQuery("DESCRIBE customers");
         while (resultSet.next()){
            System.out.println(resultSet.getString(1)+" "+resultSet.getString(2)+" "
                    +resultSet.getString(3)+ " "+ resultSet.getString(4));
         }
         connection.close();
        }
         catch (Exception e) {
         System.out.println(e);
      }
   }
}      

输出

获得的输出如下所示：

Connected successfully...!
Primary key created successfully...!
cust_ID int NO UNI
cust_Name varchar(30) YES 
cust_login_ID int NO PRI

import mysql.connector
#establishing the connection
connection = mysql.connector.connect(
    host='localhost',
    user='root',
    password='password',
    database='tut'
)
cursorObj = connection.cursor()
# Create table 
primary_key_query = '''CREATE TABLE TEST (ID INT NOT NULL, NAME VARCHAR (20) NOT NULL, AGE INT NOT NULL, PRIMARY KEY (ID))'''
cursorObj.execute(primary_key_query)
connection.commit()
print("Primary key column is created successfully!")
cursorObj.close()
connection.close()     

输出

以上代码的输出如下：

Primary key column is created successfully!