Think\Db\Query::parseExpress PHP Method

    protected function parseExpress()
    {
        $options = $this->options;
        // 获取数据表
        if (empty($options['table'])) {
            $options['table'] = $this->getTable();
        }
        if (!isset($options['where'])) {
            $options['where'] = [];
        } elseif (isset($options['view'])) {
            // 视图查询条件处理
            foreach (['AND', 'OR'] as $logic) {
                if (isset($options['where'][$logic])) {
                    foreach ($options['where'][$logic] as $key => $val) {
                        if (array_key_exists($key, $options['map'])) {
                            $options['where'][$logic][$options['map'][$key]] = $val;
                            unset($options['where'][$logic][$key]);
                        }
                    }
                }
            }
            if (isset($options['order'])) {
                // 视图查询排序处理
                if (is_string($options['order'])) {
                    $options['order'] = explode(',', $options['order']);
                }
                foreach ($options['order'] as $key => $val) {
                    if (is_numeric($key)) {
                        if (strpos($val, ' ')) {
                            list($field, $sort) = explode(' ', $val);
                            if (array_key_exists($field, $options['map'])) {
                                $options['order'][$options['map'][$field]] = $sort;
                                unset($options['order'][$key]);
                            }
                        } elseif (array_key_exists($val, $options['map'])) {
                            $options['order'][$options['map'][$val]] = 'asc';
                            unset($options['order'][$key]);
                        }
                    } elseif (array_key_exists($key, $options['map'])) {
                        $options['order'][$options['map'][$key]] = $val;
                        unset($options['order'][$key]);
                    }
                }
            }
        }
        if (!isset($options['field'])) {
            $options['field'] = '*';
        }
        if (!isset($options['strict'])) {
            $options['strict'] = $this->getConfig('fields_strict');
        }
        foreach (['master', 'lock', 'fetch_class', 'fetch_sql', 'distinct'] as $name) {
            if (!isset($options[$name])) {
                $options[$name] = false;
            }
        }
        foreach (['join', 'union', 'group', 'having', 'limit', 'order', 'force', 'comment'] as $name) {
            if (!isset($options[$name])) {
                $options[$name] = '';
            }
        }
        if (isset($options['page'])) {
            // 根据页数计算limit
            list($page, $listRows) = $options['page'];
            $page = $page > 0 ? $page : 1;
            $listRows = $listRows > 0 ? $listRows : (is_numeric($options['limit']) ? $options['limit'] : 20);
            $offset = $listRows * ($page - 1);
            $options['limit'] = $offset . ',' . $listRows;
        }
        $this->options = [];
        return $options;
    }