<?php
namespace core\db;

/**
 * SQL 辅助类
 */
class Sql
{
    // 构建 INSERT 语句
    public static function insert($table, $data)
    {
        $fields = implode(', ', array_keys($data));
        $placeholders = ':' . implode(', :', array_keys($data));
        return 'INSERT INTO ' . $table . ' (' . $fields . ') VALUES (' . $placeholders . ')';
    }

    // 构建 UPDATE 语句
    public static function update($table, $data, $where = '')
    {
        $set = array();
        foreach ($data as $key => $value) {
            $set[] = $key . ' = :' . $key;
        }
        $sql = 'UPDATE ' . $table . ' SET ' . implode(', ', $set);
        if ($where) {
            $sql .= ' WHERE ' . $where;
        }
        return $sql;
    }

    // 构建 SELECT 语句
    public static function select($table, $fields = '*', $where = '', $order = '', $limit = '')
    {
        $sql = 'SELECT ' . $fields . ' FROM ' . $table;
        if ($where) {
            $sql .= ' WHERE ' . $where;
        }
        if ($order) {
            $sql .= ' ORDER BY ' . $order;
        }
        if ($limit) {
            $sql .= ' LIMIT ' . $limit;
        }
        return $sql;
    }

    // 构建 DELETE 语句
    public static function delete($table, $where = '')
    {
        $sql = 'DELETE FROM ' . $table;
        if ($where) {
            $sql .= ' WHERE ' . $where;
        }
        return $sql;
    }
}