php 如何检查 MySQL 数据库中是否存在值
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How to Check if value exists in a MySQL database
提问by Hatim
Suppose I have this table:
假设我有这个表：
id | name | city
------------------
1 | n1 | c1
2 | n2 | c2
3 | n3 | c3
4 | n4 | c4
I want to check if the value c7exists under the variable cityor not.
我想检查c7变量下是否存在该值city。
If it does, I will do something.
If it doesn't, I will do something else.
如果是这样，我会做些什么。
如果没有，我会做其他事情。
回答by Reinder Wit
preferred way, using MySQLi extension:
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();
deprecated:
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...
}
回答by Blaster
For Exact Match
精确匹配
"SELECT * FROM yourTable WHERE city = 'c7'"
For Pattern / Wildcard Search
对于模式/通配符搜索
"SELECT * FROM yourTable WHERE city LIKE '%c7%'"
Of course you can change '%c7%'to '%c7'or 'c7%'depending on how you want to search it. For exact match, use first query example.
当然，您可以更改'%c7%'为'%c7'或'c7%'取决于您要搜索的方式。对于完全匹配，请使用第一个查询示例。
PHP
PHP
$result = mysql_query("SELECT * FROM yourTable WHERE city = 'c7'");
$matchFound = mysql_num_rows($result) > 0 ? 'yes' : 'no';
echo $matchFound;
You can also use ifcondition there.
您也可以if在那里使用条件。
回答by Hari
Assuming the connection is established and is available in global scope;
假设连接已建立并且在全局范围内可用；
//Check if a value exists in a table
function record_exists ($table, $column, $value) {
global $connection;
$query = "SELECT * FROM {$table} WHERE {$column} = {$value}";
$result = mysql_query ( $query, $connection );
if ( mysql_num_rows ( $result ) ) {
return TRUE;
} else {
return FALSE;
}
}
Usage: Assuming that the value to be checked is stored in the variable $username;
用法：假设要检查的值存储在变量$username中；
if (record_exists ( 'employee', 'username', $username )){
echo "Username is not available. Try something else.";
} else {
echo "Username is available";
}
回答by Hassam Satti
For Matching the ID:
匹配ID：
Select * from table_name where 1=1
For Matching the Pattern:
匹配模式：
Select * from table_name column_name Like '%string%'
回答by Muhammad Raheel
SELECT
IF city='C7'
THEN city
ELSE 'somethingelse'
END as `city`
FROM `table` WHERE `city` = 'c7'
回答by mushkincode
I tried to d this for a while and
$sqlcommand = 'SELECT * FROM database WHERE search="'.$searchString.'";';just works if there are TWO identical entries, but,
if you replace
$sth = $db->prepare($sqlcommand);
$sth->execute();
$record = $sth->fetch();
if ($sth->fetchColumn() > 0){}if ($sth->fetchColumn() > 0){}with
if ($result){}it works with only one matching record, hope this helps.
我尝试了一段时间，
如果有两个相同的条目，
它就可以工作，但是，如果你
用它替换它，
它只适用于一个匹配的记录，希望这会有所
帮助。 $sqlcommand = 'SELECT * FROM database WHERE search="'.$searchString.'";';
$sth = $db->prepare($sqlcommand);
$sth->execute();
$record = $sth->fetch();
if ($sth->fetchColumn() > 0){}if ($sth->fetchColumn() > 0){}if ($result){}
