MySQL query to get column names?

Question

I\'d like to get all of a mysql table\'s col names into an array in php?

Is there a query for this?

Answer 1

SHOW COLUMNS in mysql 5.1 (not 5.5) uses a temporary disk table.

• http://dev.mysql.com/doc/refman/5.1/en/internal-temporary-tables.html
• http://dev.mysql.com/doc/refman/5.1/en/show-columns.html

So it can be considered slow for some cases. At least, it can bump up your created_tmp_disk_tables value. Imagine one temporary disk table per connection or per each page request.

SHOW COLUMNS is not really so slow, possibly because it uses file system cache. Phpmyadmin says ~0.5ms consistently. This is nothing compared to 500ms-1000ms of serving a wordpress page. But still, there are times it matters. There is a disk system involvement, you never know what happens when server is busy, cache is full, hdd is stalled etc.

Retrieving column names through SELECT * FROM ... LIMIT 1 was around ~0.1ms, and it can use query cache as well.

So here is my little optimized code to get column names from a table, without using show columns if possible:

function db_columns_ar($table)
{
//returns Array('col1name'=>'col1name','col2name'=>'col2name',...)
if(!$table) return Array();
if(!is_string($table)) return Array();

global $db_columns_ar_cache;
if(!empty($db_columns_ar_cache[$table]))
    return $db_columns_ar_cache[$table];


//IMPORTANT show columns creates a temp disk table
$cols=Array();
$row=db_row_ar($q1="SELECT * FROM `$table` LIMIT 1");
if($row)
    {
    foreach($row as $name=>$val)
        $cols[$name]=$name;
    }
else
    {
    $coldata=db_rows($q2="SHOW COLUMNS FROM `$table`");
    if($coldata)
        foreach($coldata as $row)
            $cols[$row->Field]=$row->Field;
    }
$db_columns_ar_cache[$table]=$cols;
//debugexit($q1,$q2,$row,$coldata,$cols);
return $cols;
}

Notes:

• As long as your tables first row does not contain megabyte range of data, it should work fine.
• The function names db_rows and db_row_ar should be replaced with your specific database setup.