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[mySQL]关于add table的一个注意小事项，直接影响后续populate table

2017-02-23 06:46 295 查看

<!DOCTYPE html>
<html lang="en">

<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Add a table to database</title>
<link href="css/bootstrap.min.css" rel="stylesheet">
<style>
h1 {
color: purple;
}

h3 {
color: #42d5ce;
}

.containingDiv {
border: 1px solid #7c73f6;
margin-top: 100px;
border-radius: 15px;
}
</style>

</head>

<body>
<div class="container-fluid">
<div class="row">
<div class="col-sm-offset-1 col-sm-10 containingDiv">
<h1>Add a table to database:</h1>
<h3>Connect to database</h3>
<?php
//mysqli_connect(host, username, password, dbname)
$link = @mysqli_connect("localhost", "cdwccdwc_user", "bobo1989..", "cdwccdwc_users") or die("ERROR: Unable to connect: " . mysqli_connect_error());

echo "<p>Connected successfully to the database.</p>";
?>

<h3>Create table</h3>
<?php
$sql = "CREATE TABLE users3(ID INT(4) NOT NULL PRIMARY KEY AUTO_INCREMENT, firstname CHAR(20) NOT NULL, lastname CHAR(20) NOT NULL, email VARCHAR(30), password VARCHAR(40))";//AUTO_INCREMENT is very important,because if not add it, you can just insert all the values only once.
if(mysqli_query($link, $sql)){
echo "<p>Table users created successfuly!</p>";
}else{
echo "ERROR: Unable to execute $sql" . mysqli_error($link);
}
?>

</div>
</div>
</div>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>
<script src="js/bootstrap.min.js"></script>
</body>

</html>

如图，红色加粗标记的AUTO_INCREMENT,在创建table的时候加与不加的区别在于：

加AUTO_INCREMENT：后续populate table 的时候可以添加任意数量的表行内容，因为entry for key "primary"在自动增加

不加AUTO_INCREMENT：上面操作只能添加一次，会报错，例如：ERROR: Unable to excecute: INSERT INTO users3 (firstname, lastname, email,
password) VALUES ('tom', 'cluz', 'tm@gmial.com', 'ef0c0fd6710ab42cd8595bee67c65424'). Duplicate entry '0' for key 'PRIMARY'。

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