查询MySQL数据库

Question

I have this database I created with a phpMyAdmin client. Specific queries like SELECT * FROM TagData LIMIT 0,10 in my php code runs perfect. But when I add a wildcard to the query like SELECT * FROM TagData WHERE Device_Name LIKE 'Valve%' LIMIT 0,10 it doesn't work. The strange thing is that the exact same SQL works perfect in the phpMyAdmin tool.

This is how I run my query in php:

$query="SELECT * FROM TagData WHERE Device_Name LIKE 'Valve%' LIMIT 0,10";
$tmpResult=mysql_query(sprintf($query));

I have a strong feeling that the quote characters in the $query string are the problem. Can someone please explain me what I am doing wrong and why I am doing this wrong.

The result mysql_error() gives is:

Query was empty

Answer 1

You dont need sprintf when you dont insert any custom parameters. Just leave it raw.

Your query was emtpy because the string you gave to sprintf was malformed and sprintf returned null/ an empty string.

You need parameters to place in sprintf otherwise this has no use. And % is a control character for sprintf, to escape this you would have to place %% instead of % but my advice here ins aslong as you do not have any parameters, just dont use it!

To make your query work just fire it raw

$query= "SELECT * FROM TagData WHERE Device_Name LIKE 'Valve%' LIMIT 0,10";
$tmpResult = mysql_query($query);

And now, please have a look what sprintf actually does:

http://php.net/manual/en/function.sprintf.php

However please consider upgrading to MySQLi or PHP/PDO extension because MySQL class is outdated, deprecated, unsave, slow and will be removed from PHP in the future.

http://php.net/manual/en/book.mysqli.php

http://php.net/manual/en/book.pdo.php