MySQL string function substring: string intercept

MySQL string intercept function: Left (), right (), substring (), Substring_index (). There is also mid (), substr (). where mid (), substr () is equivalent to the substring () function, the function of substring () is very powerful and flexible.

1. String intercept: Left (str, length)

Mysql> Select Left (' example.com ', 3);
+-------------------------+
| Left (' example.com ', 3) |
+-------------------------+
| Exa |
+-------------------------+
2. String intercept: Right (str, length)

Mysql> Select Right (' example.com ', 3);
+--------------------------+
| Right (' example.com ', 3) |
+--------------------------+
| com |
+--------------------------+

Instance:

#查询某个字段后两位字符
Select Right (LAST3, 2) as Last2 from Historydata limit 10;
#从应该字段取后两位字符更新到另外一个字段
Update ' historydata ' Set ' Last2 ' =right (LAST3, 2);

3. String interception: Substring (str, POS); SUBSTRING (str, POS, len)

3.1 starts at the 4th character position of the string until the end.

mysql> Select substring (' example.com ', 4);
+------------------------------+
| SUBSTRING (' example.com ', 4) |
+------------------------------+
| ple.com |
+------------------------------+
3.2 starts at the 4th character position of the string and takes only 2 characters.

mysql> Select substring (' example.com ', 4, 2);
+---------------------------------+
| SUBSTRING (' example.com ', 4, 2) |
+---------------------------------+
| PL |
+---------------------------------+
3.3 Starts from the 4th character position (reciprocal) of the string until it ends.

mysql> Select substring (' example.com ',-4);
+-------------------------------+
| SUBSTRING (' example.com ',-4) |
+-------------------------------+
|. com |
+-------------------------------+
3.4 is taken from the 4th character position (reciprocal) of the string and takes only 2 characters.

mysql> Select substring (' example.com ',-4, 2);
+----------------------------------+
| SUBSTRING (' example.com ',-4, 2) |
+----------------------------------+
|. C |
+----------------------------------+
We notice that in function substring (str,pos, len), POS can be negative, but Len cannot take a negative value.

4. String interception: Substring_index (Str,delim,count)

4.1 Intercept all characters before the second '. '.

Mysql> Select Substring_index (' www.example.com ', '. ', 2);
+------------------------------------------------+
| substring_index (' www.example.com ', '. ', 2) |
+------------------------------------------------+
| www                                    |
+------------------------------------------------+
4.2 intercepts all characters after the second '. ' (Countdown).

Mysql> Select Substring_index (' www.example.com ', '. ',-2);
+-------------------------------------------------+
| substring_index (' www.example.com ', '. ',-2) |
+-------------------------------------------------+
| com.cn                                            |
+-------------------------------------------------+
4.3 Returns the entire string if the value specified by the Delim parameter is not found in the string

Mysql> Select Substring_index (' www.example.com ', '. CoC ', 1);
+---------------------------------------------------+
| Substring_index (' www.example.com ', '. CoC ', 1) |
+---------------------------------------------------+
| www.example.com |
+---------------------------------------------------+

MySQL string function substring: string intercept