php mysql select语句

Question

I am having difficulties with a MYSQl select statement. Is it possible to return a value where the right value's match. eg. I have a table.

id |   1   |   2   |   3   | etc. <--- COLUMNS
1  | Value | Value | Value | etc.
2  | Value | Value | etc.. 
3  | Value | Value |
4  | Value | Value |
5  | Value | Value | etc...

Im am trying through php to query the database to return value with.

$id = 3;
$inputvalues = "SELECT 'column'
FROM `DB`
WHERE `id` = $id
";

$return = mysql_query($inputvalues, $connection);


while ($r = mysql_fetch_array($return)){
$r[0]; 
echo "$loc = $row[3]<br />";

I think in theory this should work however all the returned value's come back empty?

Is this possible?

Answer 1

You shouldn't use single quotes ( ' ) around the column names, you can use backticks ( ` ).

SELECT column
FROM `DB`
WHERE `id` = '$id'

or

SELECT `column`
FROM `DB`
WHERE `id` = '$id'

Put together:

$id = 3;
$sql = "SELECT column
        FROM `DB`
        WHERE `id` = '$id'";

$return = mysql_query($inputvalues, $connection);

while ($r = mysql_fetch_array($return)) {
  print_r($r);
}

Answer 2

Have you tried your query in a DB editor like MySql Workbench?

Your query should look like the following:

 "SELECT column FROM DB WHERE id = '$id'"

You must surround the value with single quotes, not around the column name.

Answer 3

If your columns are loaded dynamically don't use quotes around variable in php

$id = 3;
$sql = "SELECT {$column}
        FROM `DB`
        WHERE `id` = '$id'";

it seems like variable name isn't replaced with actual value in query