学习的时候我喜欢对比，MySQL和Oracle比，Python和MySQL比，总能有一些收获，也有了新的理解。

今天整理这部分内容的时候，我发现Python和MySQL还是有很多相似之处。学习一门语言，一个数据库，字符串的处理都是一个相对重要的部分，所以我决定对比一下两者的差别。

下面的演示会一边Python,一边MySQL,所以按照这个思路来看就不会感觉突兀了。

转义字符

>>> print '\\'
\

mysql> select '\\';
+---+
| \ |
+---+
| \ |
+---+

>>> print '\"'
"
mysql> select '\"';
+---+
| " |
+---+
| " |
+---+

>>> print '\''
'
mysql> select '\'';
+---+
| ' |
+---+
| ' |
+---+

字符串拼接
>>> x = 'hello'
>>> y = 'tester'
>>> z = x + y
>>> print z
hellotester

set @x='hello';
set @y='tester';
mysql> select @x;
+-------+
| @x    |
+-------+
| hello |
mysql> select @y;
+--------+
| @y     |
+--------+
| tester |
+--------+
mysql> select concat(@x,@y);
+---------------+
| concat(@x,@y) |
+---------------+
| hellotester   |
+---------------+

字符串复制
>>> print '#'*20
####################
mysql> select repeat('#',20);
+----------------------+
| repeat('#',20)       |
+----------------------+
| #################### |
+----------------------+

>>> print ' '*20 + 'end'
                    end
mysql> select space(20);
+----------------------+
| space(20)            |
+----------------------+
|                      |
+----------------------+
                    

字符串截取
>>> name = 'yangjianrong'
>>> name[0]
'y'

>>> name[-1]
'g'
>>> name[1]
'a'
>>> name[1:4]
'ang'

>>> name[:]
'yangjianrong'
>>>
>>> name[1:4:2]
'ag'

mysql> set @name:='yangjianrong';
mysql> select left(@name,1);         
+---------------+
| left(@name,1) |
+---------------+
| y             |
+---------------+
mysql> select right(@name,1);
+----------------+
| right(@name,1) |
+----------------+
| g              |
+----------------+
mysql> select substring(@name,2,3);
+----------------------+
| substring(@name,2,3) |
+----------------------+
| ang                  |
+----------------------+
mysql> select substring(@name,1);
+--------------------+
| substring(@name,1) |
+--------------------+
| yangjianrong       |
+--------------------+
或者使用mid
mysql> select mid(@name,2,3);         
+----------------+
| mid(@name,2,3) |
+----------------+
| ang            |
+----------------+
mysql>  select mid(@name,1);         
+--------------+
| mid(@name,1) |
+--------------+
| yangjianrong |
+--------------+

>>> name
'yangjianrong'

>>> print '%s' %name
yangjianrong

字符串格式化，匹配
>>> '{name},{alias}'.format(name='yangjianrong',alias='jeanron100')    
'yangjianrong,jeanron100'
>>>

mysql>  select concat(insert(@name,1,4,'yangjianrong'),insert(@alias,1,5,'jeanron100')) comm;
+------------------------+
| comm                   |
+------------------------+
| yangjianrongjeanron100 |
+------------------------+


字符串长度>>> ba
'this is a test bar'
>>> len(ba)
18
mysql> select length(@ba);

字符串空格处理

>>> s = ' abc '
>>> s.lstrip()
'abc '
>>> s.rstrip()
' abc'
>>> s.strip()
'abc'
>>>
mysql> set @s=' abc ';
Query OK, 0 rows affected (0.00 sec)
mysql> select ltrim(@s);
+-----------+
| ltrim(@s) |
+-----------+
| abc       |
+-----------+
1 row in set (0.00 sec)

mysql> select rtrim(@s);
+-----------+
| rtrim(@s) |
+-----------+
|  abc      |
+-----------+
1 row in set (0.00 sec)

mysql> select trim(@s);
+----------+
| trim(@s) |
+----------+
| abc      |
+----------+
1 row in set (0.00 sec)

字符串匹配
>>> l = ['a','b','c']
>>> ''.join(l)
'abc'
>>> '*'.join(l)
'a*b*c'

mysql> select concat_ws(',','a','b','c','d','e') comm;
+-----------+
| comm      |
+-----------+
| a,b,c,d,e |
+-----------+


>>> s = 'a b c d e '
>>> s.split(' ')
['a', 'b', 'c', 'd', 'e', '']
mysql> set @s='a b c d e ';
Query OK, 0 rows affected (0.00 sec)

mysql> select replace(@s,' ',',');
+---------------------+
| replace(@s,' ',',') |
+---------------------+
| a,b,c,d,e,          |
+---------------------+

字符串复制
>>> s = 'aabbcc'
>>> s.replace('aa','tt')
'ttbbcc'

mysql> set @s='aabbcc';
Query OK, 0 rows affected (0.00 sec)

mysql> select replace(@s,'aa','tt');
+-----------------------+
| replace(@s,'aa','tt') |
+-----------------------+
| ttbbcc                |
+-----------------------+

 字符串编码
>>> s.encode('utf8')
'aabbcc'

mysql> select  convert(@s using utf8);
+------------------------+
| convert(@s using utf8) |
+------------------------+
| aabbcc                 |
+------------------------+

判断字符串开始匹配的字符
>>> s.startswith('aa')
True

mysql> SELECT LOCATE('aa',@s,1);  
+-------------------+
| LOCATE('aa',@s,1) |
+-------------------+
|                 1 |
+-------------------+