您的创建表语法错误，应为：

Your create table syntax is wrong, should be:

 $sql = 'CREAT TABLE '.$table_name.'(
-----
 $sql = 'CREATE TABLE '.$table_name.'(

编辑：定义主键

 $sql = 'CREATE TABLE '.$table_name.'(
        id INTEGER NOT NULL,
        thumbs_max VARCHAR(3),
        image_max VARCHAR(4),
        image_quality VARCHAR(3),
        PRIMARY KEY (id))';

来自W3schools的SQL的其他信息： http://www.w3schools.com/sql/sql_primarykey.asp

Bit of extra info on SQL from W3schools: http://www.w3schools.com/sql/sql_primarykey.asp