mysql 问题汇总

1、 oracle 中的 查询语句 自动产生顺序的排序，而mysql不行

mysql> select * from tags;
+-------+-------+
| docid | tagid |
+-------+-------+
|     1 |     1 |
|     1 |     3 |
|     1 |     5 |
|     1 |     7 |
|     2 |     2 |
|     2 |     4 |
|     2 |     6 |
|     3 |    15 |
|     4 |     7 |
|     4 |    40 |
+-------+-------+
10 rows in set (0.07 sec)
 
mysql> set @num=0;
Query OK, 0 rows affected (0.00 sec)
 
mysql> select @num:=@num+1,docid,tagid from tags;
+--------------+-------+-------+
| @num:=@num+1 | docid | tagid |
+--------------+-------+-------+
|            1 |     1 |     1 |
|            2 |     1 |     3 |
|            3 |     1 |     5 |
|            4 |     1 |     7 |
|            5 |     2 |     2 |
|            6 |     2 |     4 |
|            7 |     2 |     6 |
|            8 |     3 |    15 |
|            9 |     4 |     7 |
|           10 |     4 |    40 |
+--------------+-------+-------+
10 rows in set (0.01 sec)
 
mysql>

2、查询包含汉字、查询前十个、查询表中字段类型

查看表中各个字段类型和备注
select column_name,column_comment,data_type from information_schema.columns where table_name='stockdates';

Alter table stockdates modify pe integer default NULL;

select chg from stockdates where chg like '%[吖-座]%'  limit 10;

3、Python连接mysql中文输出乱码，在连接数据的连接参数里加上字符集说明查询出的结果的编码，这个不加的后果可能是查询出的汉字字符都是问号

conn=pymssql.connect(server='.',user='', password='',database='MyTest',charset='utf8')