PHP Method Chaining with Database Sample.

db.php

<?php
class DB
{
    private $select;
    private $where;
    private $where_and;
    private $where_or;

    public function select($select, $fields)
    {
        $this->select = "SELECT $fields FROM $select";
        return $this;
    }

    public function where($condition, $eq)
    {
        $this->where .= " $condition=$eq " ;
        return $this;
        
    }

    public function where_and($condition, $eq)
    {
        $this->where_and .= " AND $condition=$eq " ;
        return $this;
        
    }

    public function where_or($condition, $eq)
    {
        $this->where_or .= " OR $condition=$eq " ;
        return $this;
        
    }

    public function show_query()
    {
        $where = ($this->where) ? " WHERE " : ' ';

        $query = $this->select;
        $query .= $where;
        $query .= $this->where;
        $query .= $this->where_and;
        $query .= $this->where_or;

        return $query;
    }
}

$db = new DB();

echo $db->select('users as u', 'ali')
                        ->where('u.username', 'admin')
                        ->where_and('u.password', '123456')
                        ->where_and('u.isAdmin', true)
                        ->show_query();

/*
Output: SELECT ali FROM users as u WHERE u.username=admin AND u.password=123456 AND u.isAdmin=1
*/