Retrieve the column names from an empty MySQL query result

Question

Is there a way to retrieve the column names of a query that returns no data?

I'm using (somewhat) complicated queries such as:

SELECT 
    i.*,
    ic1.permalink as category_permalink, 
    ic1.title as category_title,
    ic1.sid as category_sid,
    ic2.permalink as hook_category_permalink,
    ic2.title as hook_category_title,
    ic2.sid as hook_category_sid
FROM item i
    LEFT JOIN item_to_item_category itic ON i.sid = itic.item_sid
    LEFT JOIN item_category ic1 ON ic1.sid = itic.item_category_sid
    LEFT JOIN item_category ic2 ON ic1.hook = ic2.sid
WHERE i.uid = ''
LIMIT 0,1 

The result of this query would be empty because of WHERE i.uid = "" . Is there a way how to find the column names when there's no result?

Please note that I'm aware of solutions using DESCRIBE and select column_name from information_schema.columns where table_name='person'; but I need a more flexible solution that will fit these multicolumn queries.

Please also note that I am still using the original PHP MySQL extention (so no MySQLi, and no PDO).

Anyone?

Answer 1

For PDO, try PDOStatement->getColumnMeta() . For mysqli, there's mysqli_result->fetch_fields() , mysqli_result->fetch_field() and mysqli_result->fetch_field_direct() . For mysql, replace it with PDO or mysqli.

Answer 2

Here is a simple class based on mysqli . This method will work on empty tables as well. Of course, add your own error checking as needed.

Success will return a numerically indexed array of column names from $table.
Failure or non-string input will return . 。

class mysqlz extends mysqli {

    function fetch_table_columns($table) {
        if(!is_string($table)) {
            return false;
        } elseif($obj = $this->query("SHOW COLUMNS FROM " . $table)) {
                while($fields = $obj->fetch_object()) {
                    $columns[] = $fields->Field;
                }
                return $columns;
        } else {
            return false;
        }
    }
}

To use, first instantiate your database as usual:
$mysql = new mysqlz($host, $user, $pass, $database);

Then, call the method to retrieve the column names:
$columns = $mysql->fetch_table_columns("table_name_here");

Depending on your table, the resulting array should similar to this: 类似：

array(3) { [0]=> string(2) "id" [1]=> string(10) "first_name" [2]=> string(9) "last_name" }

If method returns false (var_dump returns bool(false) ) you can check the current error with $mysqlz->error . For more information on error checking, take a look at the PHP mysqli manual at http://www.php.net/manual/en/book.mysqli.php .

Answer 3

Assuming you are calling the query from PHP. You can call mysqli_fetch_fields even with an emtpy query.

Answer 4

For AdoDB you can use:

$db->Execute("SELECT .......");  
$colInfo = $res->FieldTypesArray(); 

The output is similar to method MetaColumns($table) , but you can use it on every result set not only for tables (including joins). It works for empty results or empty tables too.

Thanks to outis , I found this function after searching "fetch_field()" in adoDBs mysql-driver :D