Simple Crud in PHP

crud.php

<?php 
	function insert($table = '1', $values = array(' ' => ' ')){
		if (is_array($values)){
			foreach($values as $value){
				$field .= "$value,";
			}
		}
		$val = str_replace(',', '', $val);
		
		$query = "INSERT INTO $table VALUES ($val)";
		$this->exec($query);
	}
	
	function delete($table = '1', $condition = array(' ' => ' ')){
		foreach ($condition as $key => $value)
			$where .= " $key='$value' ";
		}
		$where = str_replace(',', '', $where);
		$where = str_replace('AND', '', $where);
		$where = str_replace('OR', '', $where);
		
		$query = "DELETE FROM $table WHERE $where";
		$this->exec($query);
	}
	function update($table = '1', $set $condition = array(' ' => ' ')){
		foreach ($condition as $key => $value){
			$set .= " $key='$value', "
		}
		$set = str_replace(',', '', $set);
		foreach ($condition as $key => $value)
			$where .= " $key='$value' ";
		}
		$where = str_replace(',', '', $where);
		$where = str_replace('AND', '', $where);
		$where = str_replace('OR', '', $where);
		
		$query = "UPDATE $table SET $set WHERE $where";
		$this->exec($query);
	}
	function run(){
		$sql = $this->sql;
		$sql->execute($query);
	}