MySQLi helper functions I use to describe and understand tables. Great for Magento.

_mysqli_helper.php

<?php 
//  (c) Chris Kelley of "Tech Nerd Chris", technerdchris at gmail
//  This is my dev code to speed understanding of databases. Put up a search form
//  and use this to render HTML results of table structures
//
//  $db = mysqli handle
//  optional $tbl_order lets you send in table names as an array to set order or limit results
function describe( $db, $tbl_order='' ){
	$_colors =array( 'red' => "red", 'orn' => "orange", 'blue' => "#06f", 'gray' => "#666", 'grn' => "#0a3" );
	foreach( $_colors as $var => $_c )
		if( !isset($$var) )
			$$var = " style=\"color:$_c\" ";

	echo "<fieldset style=\"display: inline-block;border:none\">";
	
	$sql="SELECT database() AS 'db_name'";
	$db_name=oneRow($db, $sql);
	$db_name=$db_name['db_name'];	
	
	$sql ="SELECT TABLE_NAME AS 'table', TABLE_ROWS AS 'rows' FROM information_schema.TABLES ";
	$sql.="WHERE TABLES.TABLE_SCHEMA = '$db_name' AND TABLES.TABLE_TYPE = 'BASE TABLE'";
	$show_tables=multiRow($db,$sql);
	$err=mysqli_error($db);
	if(strlen($err)) 
		echo($sql."\nError description: $err\n" );

	if( count( $show_tables) > 0 ) {
		foreach($show_tables as $arr){
			$_tbl=$arr['table'];
			$_rws=$arr['rows'];
			$tables[$_tbl]['table']=$_tbl;
			$tables[$_tbl]['rows']=$_rws;
		}
	} 	
	$tbl_order = array();
	if( strlen($tbl_order) > 5 ) 
		$tbl_order = explode( ',', $tbl_order);
	else
		$tbl_order=array_keys($tables);

	$keys = array('Field','Type','Null','Key','Default','Extra');  

	$fieldname_width=0;

	echo "<h4>database `$db_name`</h4>";
	foreach( $tbl_order AS $table ){
		$sql="SHOW FULL COLUMNS FROM $table";
		$_desc=multiRow($db, $sql);

		// Process the output
		foreach( $_desc as $idx => $col ) {
			// determine max fieldname width
			if( strlen( $col['Field'] ) > $fieldname_width )
				$fieldname_width=strlen( $col['Field'] );		
		}
		$fieldname_width+=2;	// add padding for the ` `
		$_f = sprintf( "%%%ds", $fieldname_width );

		printf("<div style=\"float:left;border:solid thin #666;padding:3px\">");
		echo "<pre>";
		echo "<h4>$table </h4>";
		num_records( $db, $table );
		$table_format_string = "$_f <small $gray>%-14.14s</small> %4s %3s <small><span $blue>%s</span> <span>%s</span> <span $orn>%s</span></small>\n";
		printf(  $table_format_string, 'Field','Type','Null','Key','Default ','Extra', 'Comment' );
		foreach( $_desc as $col ) {
			printf( $table_format_string
					, '`'.$col['Field'].'`'
					, $col['Type']
					, $col['Null'] =='YES' ? 'yes' : "  <span $red>NO</span>"
					, $col['Key']
					, strlen($col['Default']) > 0 ? $col['Default']." " : "<small $blue>┈ </small> "
					, strlen($col['Extra'])   > 0 ? $col['Extra']." "   : "<small>┈ </small> "
					, strlen($col['Comment']) > 0 ? $col['Comment']." " : "<small $orn>┈ </small> " 
			);
		}
		printf("</pre></div>" );
	}
	printf("</fieldset>");	
}

//  $db=mysqli handle, $findfield is what you're searching for
//  Optional $hideZeroes: if set to true, hides tables with no rows.
//  This code is lifted from development and altered for public sharing
//  ... this fundtion calls describe() above
function table_search( $db, $findfield, $hideZeroes=0 )
{
  $sql="SELECT database() AS 'db_name'";
  $db_name=oneRow($db, $sql);
  $db_searched=$db_name['db_name']; 

  if( $hideZeroes==true; ) {
    printf( '<P><small style="color:#666">--> hiding empty tables (which do not have any rows of data)</small></P>' );
  }
  $and_where = "";
  if (true===$hideZeroes) 
    $and_where = " AND TABLE_ROWS > 0 ";
  
  $tables=Array();
  $sql ="SELECT TABLE_NAME AS 'table', TABLE_ROWS AS 'rows' FROM information_schema.TABLES ";
  $sql.="WHERE TABLES.TABLE_SCHEMA = '$db_searched' AND TABLE_NAME LIKE '%$findfield%' $and_where AND TABLES.TABLE_TYPE = 'BASE TABLE'";
  $show_tables=multiRow($db,$sql);
  $err=mysqli_error($db);
  if(strlen($err)) 
      echo($sql."\nError description: $err\n" );
  if( count( $show_tables) > 0 ) {
    foreach($show_tables as $arr){
    	$_tbl=$arr['table'];
    	$_rws=$arr['rows'];
    	$tables[$_tbl]=$_rws;
    }
  } 	

  $cols=Array();
  $sql ="SELECT TABLE_NAME,COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS ";
  $sql.="WHERE TABLE_SCHEMA='$db_searched' AND COLUMN_NAME LIKE '%$findfield%'";
  $show_tables=multiRow($db,$sql);
  $err=mysqli_error($db);
  if(strlen($err)) 
      echo($sql."\nError description: $err\n" );
  if( count( $show_tables) > 0 ) {
    foreach($show_tables as $arr){
    	$_col=sprintf( "<span $gray>%s.</span>%s", $arr['TABLE_NAME'], $arr['COLUMN_NAME'] );
    	$cols[]=$_col;
    }
  } // else echo "No results from query:\n$sql:\n";
  
  printf("<div style=\"float:left;border:solid thin red;padding:3px\"><pre>");
  if (count($tables)) {
    printf("%d tables with '%s' in the name:\n", count($tables), $findfield);
    foreach($tables as $name=>$count ) 
      printf("\t%s <small style=\"color:#666\">[%d]</small>\n", $name, $count);
  } else 
    echo "No tables have '$findfield' in their name.\n";
  printf("</pre></div>" );
  
  printf("<div style=\"float:left;border:solid thin green;padding:3px;margin-left:5px\"><pre>");
  if (count($cols) > 0) {
    printf("%d fieldnames with '%s' in their name:\n\t%s\n", count($cols), $findfield, implode("\n\t",$cols));
  } else 
    echo "No columns have '$findfield' in their name.\n";
  printf("</pre></div>" );
  printf("<div style=\"clear:both\">");
  
  if( isset($tables) && count($tables) > 0 ){
  	printf( "<P>&nbsp;</P><h3>DESCRIBE `table` for each of %d tables above...</h3>", count($tables) );
  	printf('<div>'); // style="width:1610">');
  	describe( $db, implode( ',', array_keys($tables) ));
  	('</div>');
  	printf('<div style="clear:both"></div>');
  }
}

//  $db is mysqli handle
function oneRow($db, $sql) {
	if( is_string($db) || is_null($sql) ) {
		printf( "<pre>Incorrect usage: oneRow( db handle \$db, string \$sql ) both required.</pre>\n");
		return false;
	}
	try {
		$result=$db->query($sql);
	} catch (Exception $e) {
		printf( "<pre>An error occurred: %s\n\t%s:\n\t%s</pre>\n", $e, $sql, $db->error);
	}
	$data = false;
	if( !is_bool($result) )
		$data = $result->fetch_assoc();
	return $data;
}
//  $db is mysqli handle
function multiRow($db, $sql) {
	global $red;
	if( is_string($db) || is_null($sql) ) {
		printf( "<pre>Incorrect usage: multiRow( db handle \$db, string \$sql ) both required.</pre>\n");
		return false;
	}
	$result=$db->query($sql);
	if ($result===false) {
		printf("<span>ERROR:</span>\n%s\n<span>Server response:</span> %s\n", $sql, $db->error);
		return( false );
	}
	$data = Array();
	if( !is_bool($result) )
		while( $row = $result->fetch_assoc() )
			$data[]=$row;
	return $data;
}
//  $db is mysqli handle
function query( $db, $sql ) {
	$result=$db->query($sql);
	if ($result===false) {
		printf("<span>ERROR:</span>\n%s\n<span>Server response:</span> %s\n", $sql, $db->error);
		return( false );
	}
	$_rows = $db->affected_rows;
	if( is_numeric( $_rows ) && $_rows > 0 )
		return $_rows;
	return true;
}
?>