Select.php

<?php
// /src/Php8/Sql/Select.php
namespace Php8\Sql;

use Exception;
class Select extends Where
{
    const ERR_MISSING = 'ERROR: missing FROM and/or columns';
    public $from  = '';
    public $cols  = [];
    public $order  = '';
    public $limit  = 0;
    public $offset  = 0;
    public $sql   = '';
    public function render()
    {
        // validate
        if (!($this->hasFrom() && $this->hasCols())) {
            throw new Exception(self::ERR_MISSING);
        }
        $this->sql = 'SELECT ';
        $this->sql .= implode(',', $this->cols) . ' ';
        $this->sql .= 'FROM ' . $this->from . ' ';
        if ($this->hasWhere()) {
            $this->sql .= 'WHERE ' . implode(' ', $this->where) . ' ';
        }
        if ($this->limit > 0) {
            $this->sql .= 'LIMIT ' . $this->limit . ' ';
        }
        if ($this->offset > 0) {
            $this->sql .= 'OFFSET ' . $this->offset . ' ';
        }
        return trim(str_replace('  ', ' ', $this->sql));
    }
    public function cols(array $cols) : static
    {
        $this->cols = $cols;
        return $this;
    }
    public function from(string $table) : static
    {
        $this->from = $table;
        return $this;
    }
    public function order(string $order) : static
    {
        $this->order = $order;
        return $this;
    }
    public function limit(int $num) : static
    {
        $this->limit = $num;
        return $this;
    }
    public function offset(int $num) : static
    {
        $this->offset = $num;
        return $this;
    }
    protected function hasFrom()
    {
        return (bool) $this->from;
    }
    protected function hasCols()
    {
        return (bool) $this->cols;
    }
}