MySQL NULL
НУЛЕВОЙ
Оператор MySQL IS NULL проверяет, является ли значение NULL. Если выполнено, то возвращает 1, иначе возвращает 0.
Синтаксис:
НУЛЕВОЙ
Версия MySQL: 5.6
Пример: MySQL IS NULL
В следующем операторе MySQL проверяется, являются ли 2, 0 и NULL NULL, используя оператор IS NULL.
Код:
SELECT 2 IS NULL, 0 IS NULL, NULL IS NULL;
Пример вывода:
mysql> SELECT 2 - NULL, 0 - NULL, NULL - NULL; + ----------- + ----------- + -------------- + | 2 НУЛЬ | 0 НУЛЬ | NULL IS NULL | + ----------- + ----------- + -------------- + | 0 | 0 | 1 | + ----------- + ----------- + -------------- + 1 ряд в наборе (0,00 сек)
PHP скрипт
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>example-is-null- php mysql examples | w3resource</title>
<meta name="description" content="example-is-null- php mysql examples | w3resource">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
</head>
<body>
<div class="container">
<div class="row">
<div class="col-md-12">
<h2>Testing whether a value is NULL using MySQL. It returned 1 if the value id NULL else returns 0:</h2>
<table class='table table-bordered'>
<tr>
<th>2 IS NULL</th><th>0 IS NULL</th><th>NULL IS NULL</th>
</tr>
<?php
$hostname="your_hostname";
$username="your_username";
$password="your_password";
$db = "your_dbname";
$dbh = new PDO("mysql:host=$hostname;dbname=$db", $username, $password);
foreach($dbh->query('SELECT 2 IS NULL, 0 IS NULL, NULL IS NULL') as $row) {
echo "<tr>";
echo "<td>" . $row['2 IS NULL'] . "</td>";
echo "<td>" . $row['0 IS NULL'] . "</td>";
echo "<td>" . $row['NULL IS NULL'] . "</td>";
echo "</tr>";
}
?>
</tbody></table>
</div>
</div>
</div>
</body>
</html>
JSP скрипт
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@ page import="java.sql.*" %>
<%@ page import="java.io.*" %>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>example-is-null</title>
</head>
<body>
<%
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
String Host ="jdbc:mysql://localhost:3306/w3resour_bookinfo";
Connection connection = null;
Statement statement = null;
ResultSet rs = null;
connection = DriverManager.getConnection(Host, "root", "datasoft123");
statement = connection.createStatement();
String Data ="SELECT 2 IS NULL, 0 IS NULL, NULL IS NULL";
rs = statement.executeQuery(Data);
%>
<TABLE border="1">
<tr width="10" bgcolor="#9979">
<td>2 IS NULL</td>
<td>0 IS NULL</td>
<td>NULL IS NULL</td>
</tr>
<%
while (rs.next()) {
%>
<TR>
<TD><%=rs.getString("2 IS NULL")%></TD>
<TD><%=rs.getString("0 IS NULL")%></TD>
<TD><%=rs.getString("NULL IS NULL")%></TD>
</TR>
<% } %>
</table>
<%
rs.close();
statement.close();
connection.close();
} catch (Exception ex) {
out.println("Can’t connect to database.");
}
%>
</body>
</html>
Слайд-шоу функции сравнения MySQL и операторов
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