如何检查MySQL数据库中是否存在值 [英] How to Check if value exists in a MySQL database

问题描述

假设我有这张桌子:

id | name | city
------------------
1  | n1   | c1
2  | n2   | c2
3  | n3   | c3
4  | n4   | c4

我想检查变量city下是否存在值c7.

I want to check if the value c7 exists under the variable city or not.

如果可以，我会做些什么.
如果没有，我将做其他事情.

If it does, I will do something.
If it doesn't, I will do something else.

推荐答案

首选方式，使用MySQLi扩展名:

preferred way, using MySQLi extension:

$mysqli = new mysqli(SERVER, DBUSER, DBPASS, DATABASE);
$result = $mysqli->query("SELECT id FROM mytable WHERE city = 'c7'");
if($result->num_rows == 0) {
     // row not found, do stuff...
} else {
    // do other stuff...
}
$mysqli->close();

已弃用:

$result = mysql_query("SELECT id FROM mytable WHERE city = 'c7'");
if(mysql_num_rows($result) == 0) {
     // row not found, do stuff...
} else {
    // do other stuff...
}

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