如何检查MySQL数据库中是否存在值

Question

假设我有这个表:

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

我想检查c7变量下是否存在值city.

如果是的话,我会做点什么.
如果没有,我会做点别的.

Answer 1

首选方式,使用MySQLi扩展:

$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();

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...
}

Answer 2

完全匹配

"SELECT * FROM yourTable WHERE city = 'c7'"

用于模式/通配符搜索

"SELECT * FROM yourTable WHERE city LIKE '%c7%'"

当然,您可以更改'%c7%'为'%c7'或'c7%'根据您的搜索方式.要完全匹配,请使用第一个查询示例.

PHP

$result = mysql_query("SELECT * FROM yourTable WHERE city = 'c7'");
$matchFound = mysql_num_rows($result) > 0 ? 'yes' : 'no';
echo $matchFound;

你也可以if在那里使用条件.