When a Python string encounters MySQL
When I study, I like to compare MySQL and Oracle, Python and MySQL, there is always some harvest, but also a new understanding.
While sorting through this section today, I found that Python and MySQL still have a lot in common. Learning a language, a database, and string processing are all relatively important parts, so I decided to compare the two.
The following demo will have Python and MySQL on one side, so it doesn't feel awkward to follow this line of thought.
escape character
>>> print '\\'
\
mysql> select '\\';
+---+
| \ |
+---+
| \ |
+---+
>>> print '\"'
"
mysql> select '\"';
+---+
| " |
+---+
| " |
+---+
>>> print '\''
'
mysql> select '\'';
+---+
| ' |
+---+
| ' |
+---+
string concatenation
>>> 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 |
+---------------+
string copy
>>> print '#'*20
####################
mysql> select repeat('#',20);
+----------------------+
| repeat('#',20) |
+----------------------+
| #################### |
+----------------------+
>>> print ' '*20 + 'end'
end
mysql> select space(20);
+----------------------+
| space(20) |
+----------------------+
| |
+----------------------+
string truncation
>>> 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 |
+--------------------+
Or use 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
String formatting, matching
>>> '{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 |
+------------------------+
String Length>>> ba
'this is a test bar'
>>> len(ba)
18
mysql> select length(@ba); String Space Handling
>>> 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)
string matching
>>> 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, |
+---------------------+
string copy
>>> 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 |
+-----------------------+
string encoding
>>> s.encode('utf8')
'aabbcc'
mysql> select convert(@s using utf8);
+------------------------+
| convert(@s using utf8) |
+------------------------+
| aabbcc |
+------------------------+ Determine the character at the beginning of the string match
>>> s.startswith('aa')
True
mysql> SELECT LOCATE('aa',@s,1);
+-------------------+
| LOCATE('aa',@s,1) |
+-------------------+
| 1 |
+-------------------+
