MySQL - IS NULL 运算符

要通过 JavaScript 程序在 MySQL 中执行 IS NULL 运算符，我们需要使用名为 query() 的 mysql2 函数执行带有 IS NULL 运算符的 SQL 查询，如下所示:-

sql= " SELECT column_name1, column_name2, ... FROM table_name
WHERE column_name IS NULL";
con.query(sql);

要通过 Java 程序在 MySQL 中执行 IS NULL 运算符，我们需要使用 JDBC type 4 驱动程序提供的名为 executeQuery() 的函数执行带有 IS NULL 运算符的 SQL 查询 -

String sql = "SELECT column_name1, column_name2, ... FROM table_name
WHERE column_name IS NULL";
statement.executeQuery(sql);

要通过 Python 程序在 MySQL 中执行 IS NULL 运算符，我们需要使用 MySQL Connector/Python 提供的名为 execute() 的函数执行带有 IS NULL 运算符的 SQL 查询 -

is_null_query = "SELECT column_name1, column_name2, ... FROM table_name
WHERE column_name IS NULL"
cursorObj.execute(is_null_query);

var mysql = require('mysql2');
var con = mysql.createConnection({
    host: "localhost",
    user: "root",
    password: "Nr5a0204@123"
});
 //连接到 MySQL
  con.connect(function (err) {
  if (err) throw err;
  console.log("Connected!");
  console.log("--------------------------");
 //创建数据库
  sql = "create database TUTORIALS"
  con.query(sql);
 //选择数据库
  sql = "USE TUTORIALS"
  con.query(sql);
 //创建 CUSTOMERS 表
  sql = "CREATE TABLE CUSTOMERS(ID INT NOT NULL,NAME VARCHAR(20),AGE INT,ADDRESS CHAR(25),SALARY DECIMAL(18, 2),PRIMARY KEY(ID));"
  con.query(sql);
 //插入记录
  sql = "INSERT INTO CUSTOMERS(ID, NAME, AGE, ADDRESS, SALARY) VALUES(1,'Ramesh', 32, 'Hyderabad',NULL),(2,'Khilan', 25, NULL, 1500.00),(3,'kaushik', NULL, 'Hyderabad', 2000.00),(4,'Chaital', 25, 'Mumbai', NULL),(5,'Hardik', 27, 'Vishakapatnam', 8500.00),(6, 'Komal',NULL, 'Vishakapatnam', 4500.00),(7, 'Muffy',24, NULL, 10000.00);"
  con.query(sql);
 //Using IS NULL Operator
  sql = "SELECT * FROM CUSTOMERS WHERE AGE IS NULL;"
  con.query(sql, function(err, result){
    if (err) throw err
    console.log(result)
  });
});         

输出

生成的输出如下 -

Connected!
--------------------------
[
  {
    ID: 3,
    NAME: 'kaushik',
    AGE: null,
    ADDRESS: 'Hyderabad',
    SALARY: '2000.00'
  },
  {
    ID: 6,
    NAME: 'Komal',
    AGE: null,
    ADDRESS: 'Vishakapatnam',
    SALARY: '4500.00'
  }
]         

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class IsNullOperator {
  public static void main(String[] args) {
    String url = "jdbc:mysql://localhost:3306/TUTORIALS";
    String user = "root";
    String password = "password";
    ResultSet rs;
    try {
      Class.forName("com.mysql.cj.jdbc.Driver");
            Connection con = DriverManager.getConnection(url, user, password);
            Statement st = con.createStatement();
            //System.out.println("Database connected successfully...!");
            String sql = " SELECT * FROM CUSTOMERS WHERE AGE IS NULL";
            rs = st.executeQuery(sql);
            System.out.println("Table records: ");
            while(rs.next()) {
              String id = rs.getString("Id");
              String name = rs.getString("Name");
              String age = rs.getString("Age");
              String address = rs.getString("Address");
              String salary = rs.getString("Salary");
              System.out.println("Id: " + id + ", Name: " + name + ", Age: " + age + ", Addresss: " + address + ", Salary: " + salary);
            }
    }catch(Exception e) {
      e.printStackTrace();
    }
  }
}                            

输出

获得的输出如下所示 -

Table records: 
Id: 3, Name: kaushik, Age: null, Addresss: Hyderabad, Salary: 2000.00
Id: 6, Name: Komal, Age: null, Addresss: Vishakapatnam, Salary: 4500.00             

import mysql.connector
#建立连接
connection = mysql.connector.connect(
    host='localhost',
    user='root',
    password='password',
    database='tut'
)
cursorObj = connection.cursor()
is_null_query = f"""
SELECT * FROM CUSTOMERS
WHERE AGE IS NULL;
"""
cursorObj.execute(is_null_query)
# 获取所有符合条件的行
filtered_rows = cursorObj.fetchall()
for row in filtered_rows:
    print(row)
cursorObj.close()
connection.close()                           

输出

以下是上述代码的输出 -

(3, 'kaushik', None, 'Hyderabad', Decimal('2000.00'))
(6, 'Komal', None, 'Vishakapatnam', Decimal('4500.00'))