Think\Db\Query::parseWhereExp PHP Method

    protected function parseWhereExp($logic, $field, $op, $condition, $param = [])
    {
        if ($field instanceof \Closure) {
            $this->options['where'][$logic][] = is_string($op) ? [$op, $field] : $field;
            return;
        }
        if (is_string($field) && !empty($this->options['via']) && !strpos($field, '.')) {
            $field = $this->options['via'] . '.' . $field;
        }
        if (is_string($field) && preg_match('/[,=\\>\\<\'\\"\\(\\s]/', $field)) {
            $where[] = ['exp', $field];
            if (is_array($op)) {
                // 参数绑定
                $this->bind($op);
            }
        } elseif (is_null($op) && is_null($condition)) {
            if (is_array($field)) {
                // 数组批量查询
                $where = $field;
            } elseif ($field) {
                // 字符串查询
                if (is_numeric($field)) {
                    $where[] = ['exp', $field];
                } else {
                    $where[$field] = ['null', ''];
                }
            }
        } elseif (is_array($op)) {
            $where[$field] = $param;
        } elseif (in_array(strtolower($op), ['null', 'notnull', 'not null'])) {
            // null查询
            $where[$field] = [$op, ''];
        } elseif (is_null($condition)) {
            // 字段相等查询
            $where[$field] = ['eq', $op];
        } else {
            $where[$field] = [$op, $condition];
        }
        if (!empty($where)) {
            if (!isset($this->options['where'][$logic])) {
                $this->options['where'][$logic] = [];
            }
            $this->options['where'][$logic] = array_merge($this->options['where'][$logic], $where);
        }
    }