php 检查 MySQL 行中是否存在值
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Check if value exists In MySQL row
提问by Trufa
I have a php variable: $foo
我有一个 php 变量： $foo
My MySQL table called datahas the following structure:
我的 MySQL 表调用data具有以下结构：
id var header
1 zj3 http://google.com
I would like to check if $foois all ready in varrow.
我想检查一下是否$foo都准备好了var。
If it is I would like to echo header("http://google.com")
如果是我想回声header（“http://google.com”）
How would you approach this?
你会如何处理这个问题？
Thanks in advance, please ask if any clarification is needed!
在此先感谢，请询问是否需要澄清！
回答by Rocket Hazmat
Your query should be:
您的查询应该是：
SELECT `header` FROM `data` WHERE `var` = '$foo'
This will return all the headers with a varvalue of $foo.
这将返回var值为 的所有标头$foo。
$db = mysqli_connect('localhost', 'username', 'password', 'database');
if($query = mysqli_query($db, "SELECT `header` FROM `data` WHERE `var` = '$foo'")){
while($row = mysqli_fetch_assoc($query)){
echo $row['header'];
}
mysqli_free_result($query);
}
回答by heymrcarter
first connect to the db
首先连接到数据库
$query = mysql_query("SELECT var, header FROM data WHERE id='1'") or die(mysql_error());
while($row = mysql_fetch_assoc($query)){
if($foo == $row['var']){
echo $row['header'];
}
}
EDIT: changed equality statement based on your edit
编辑：根据您的编辑更改等式语句
回答by dnagirl
are you asking if $foomatches anyof the fields in data, or if $foo=some_field? Here for if you want $foo==var.
你是问是否$foo匹配中的任何字段data，或者如果$foo=some_field？如果你想要，这里$foo==var。
$foo='somevalue';
$query="SELECT id, var, header FROM `data` WHERE var='$foo'";
$result=mysqli_query($query);
if($result->num_rows==0)
$loc= 'http://google.com';//default value for when there is no row that matches $foo
}else{
$row=$result->fetch_assoc(); //more than one row is useless since the first header('Location: x') command sends the browser to a new page and away from your script.
$loc=$row['header'];
}
header ("Location: $loc);
exit;
ETA: since you've edited your question, it appears that you want to echo the header column if your search value matches your var column. The above won't work for that.
ETA：由于您已经编辑了您的问题，如果您的搜索值与您的 var 列匹配，您似乎想要回显标题列。以上不会为此工作。
回答by brenjt
It's not difficult at all, If I understand correctly then this should help you.
这一点都不难，如果我理解正确，那么这应该对您有所帮助。
// Query Variable / Contains you database query information
$results = $query;
// Loop through like so if the results are returned as an array
foreach($results as $result)
{
if(!$result['var'])
echo $result['header'];
}
// Loop through like so if the results are returned as an object
foreach($results as $result)
{
if(!$result->var)
echo $result->header;
}
回答by Vulkan
Here's a template for all the "does it exist" questions.
这是所有“是否存在”问题的模板。
This is the only thing that actually worked for me so far and is not deprecated.
这是迄今为止唯一对我有用的东西，并且没有被弃用。
if ($query = mysqli_query($link, "SELECT header FROM data WHERE var = '$foo'")) {
$header = mysqli_fetch_assoc($query);
if ($header) {
// The variable with value $foo exists.
}
else {
// The variable with value $foo doesn't exist.
}
}
else {
// The query didn't execute for some reason. (Dammit Obama!)
}
WARNING!
警告！
Even if the variable DOES NOT EXISTthe comparison between $queryand mysqli_query()will always return TRUE.
即使变量不存在，$query和mysqli_query()之间的比较也将始终返回TRUE。
The only way --which happened to me-- for the comparison to return FALSEis because of a syntax error in your query.
比较返回FALSE的唯一方法（发生在我身上）是因为查询中存在语法错误。
I don't know why it worked for the guy who wrote the accepted answer, maybe it's an update or maybe he had a syntax error and was so confident that he didn't check if it could ever be TRUE.
我不知道为什么它对编写已接受答案的人有用，也许是更新，或者他有语法错误并且非常自信，以至于他没有检查它是否可能为TRUE。
Here's the comment someone made for correcting his syntax:
这是某人为纠正他的语法所做的评论：
"Add another ) before the { in the first line"
“在第一行的 { 之前添加另一个 )”
So, the accepted answer is WRONG!
所以，接受的答案是错误的！
回答by Mike
You just want to know if $var's value is anywhere in that column (any row(s))?
您只想知道 $var 的值是否在该列（任何行）中的任何位置？
SELECT COUNT(id) FROM data WHERE var = ?;
The result will be the number of rows for which the field var contains the value of $var.
结果将是字段 var 包含 $var 值的行数。
