1.concat函數的使用
concat(str1,str2,...)
返回的結果是參數連接後產生的字符串，如果有任何一個參數爲null，則返回結果爲null。
mysql> select concat('My','s','ql');
+-----------------------+
| concat('My','s','ql') |
+-----------------------+
| Mysql |
+-----------------------+
1 row in set (0.00 sec)
mysql> select concat('My','s','ql',null);
+----------------------------+
| concat('My','s','ql',null) |
+----------------------------+
| NULL |
+----------------------------+
1 row in set (0.00 sec)
該函數的作用就是連接字符串2.concat_ws() ：concat with separator 是CONCAT()的特殊形式。第一個參數是其它參數的分隔符。分隔符的位置放在要連接的兩個字符串間。分隔符可以是一個字符串，也可以是其它參數。如果分隔符爲 NULL，則結果爲 NULL。函數會忽略任何分隔符參數後的 NULL 值。
mysql> select concat_ws('@','My','s','ql');
+------------------------------+
| concat_ws('@','My','s','ql') |
+------------------------------+
| My@s@ql |
+------------------------------+
1 row in set (0.00 sec)
mysql> select concat_ws(';','My','s','ql');
+------------------------------+
| concat_ws(';','My','s','ql') |
+------------------------------+
| My;s;ql |
+------------------------------+
1 row in set (0.00 sec)3.REPLACE(str,from_str,to_str)函數的作用：把字符串str中的子字符串from_str全部替換爲to_str後得到的字符串，如果to_str爲空字符串，那麼相當於把from_str子字符串全去掉，如果from_str爲空字符串相當於對str不做任何修改，只要輸入參數中有null值就返回null。
mysql> select replace('mingyue-s2','-s2','');
+--------------------------------+
| replace('mingyue-s2','-s2','') |
+--------------------------------+
| mingyue |
+--------------------------------+
1 row in set (0.00 sec)
mysql> select replace('mingyue-s2','-s2',' ');
+---------------------------------+
| replace('mingyue-s2','-s2',' ') |
+---------------------------------+
| mingyue |
+---------------------------------+
1 row in set (0.00 sec)
mysql> select replace('mingyue-s2','-s2',null);
+----------------------------------+
| replace('mingyue-s2','-s2',null) |
+----------------------------------+
| NULL |
+----------------------------------+
1 row in set (0.00 sec)
mysql> select concat('mingyue','-s2');
+-------------------------+
| concat('mingyue','-s2') |
+-------------------------+
| mingyue-s2 |
+-------------------------+
1 row in set (0.00 sec)
mysql> select replace('mingyue-s2','-s2',' ');
+---------------------------------+
| replace('mingyue-s2','-s2',' ') |
+---------------------------------+
| mingyue |
+---------------------------------+
1 row in set (0.00 sec)4.TRIM([{BOTH | LEADING | TRAILING} [remstr] FROM] str)
TRIM([remstr FROM] str)
該函數的作用是在字符串str的首尾去掉子字符串remstr後得到的字符串，有以下情況：
1）如果給出LEADING關鍵字，函數將去掉str字符串最左端的子字符串remstr
2）如果給出TRAILING關鍵字，函數將去掉str字符串最右端的子字符串remstr
3）如果給出了BOTH關鍵字，函數將去掉str字符串最左右兩端的子字符串remstr
4）如果沒有關鍵字，默認爲BOTH
5）如果沒有給出子字符串，默認爲空格
mysql> SELECT TRIM(LEADING 'x' FROM 'xxxbarxxx');
+------------------------------------+
| TRIM(LEADING 'x' FROM 'xxxbarxxx') |
+------------------------------------+
| barxxx |
+------------------------------------+
1 row in set (0.04 sec)
mysql> SELECT TRIM(BOTH 'x' FROM 'xxxbarxxx');
+---------------------------------+
| TRIM(BOTH 'x' FROM 'xxxbarxxx') |
+---------------------------------+
| bar |
+---------------------------------+
1 row in set (0.00 sec)
mysql> SELECT TRIM(TRAILING 'xyz' FROM 'barxxyz');
+-------------------------------------+
| TRIM(TRAILING 'xyz' FROM 'barxxyz') |
+-------------------------------------+
| barx |
+-------------------------------------+
1 row in set (0.00 sec)
mysql> select trim(trailing '-s2' from 'mingyue-s2');
+----------------------------------------+
| trim(trailing '-s2' from 'mingyue-s2') |
+----------------------------------------+
| mingyue |
+----------------------------------------+
1 row in set (0.00 sec)
mysql> select trim('-s2' from 'mingyue-s2');
+-------------------------------+
| trim('-s2' from 'mingyue-s2') |
+-------------------------------+
| mingyue |
+-------------------------------+
1 row in set (0.00 sec)5.REVERSE(str)函數：把字符串倒序排列
mysql> select reverse('mingyue-s2');
+-----------------------+
| reverse('mingyue-s2') |
+-----------------------+
| 2s-euygnim |
+-----------------------+
1 row in set (0.00 sec)
mysql> select reverse('abc');
+----------------+
| reverse('abc') |
+----------------+
| cba |
+----------------+
1 row in set (0.00 sec)
6.LENGTH(str)函數：返回str的長度，以字節爲單位
mysql> select length('zhu');
+---------------+
| length('zhu') |
+---------------+
| 3 |
+---------------+
1 row in set (0.00 sec)
mysql> select length('mingyue-s2');
+----------------------+
| length('mingyue-s2') |
+----------------------+
| 10 |
+----------------------+
1 row in set (0.00 sec)7.LEFT(str,len)函數：返回字符串最左端的len個字符
8.RIGHT(str,len)函數：返回字符串最右端的len個字符
mysql> select left('mingyue-s2',7);
+----------------------+
| left('mingyue-s2',7) |
+----------------------+
| mingyue |
+----------------------+
1 row in set (0.00 sec)
mysql> select right('mingyue-s2',7);
+-----------------------+
| right('mingyue-s2',7) |
+-----------------------+
| gyue-s2 |
+-----------------------+
1 row in set (0.00 sec)mysql> select left('mingyue-s2',length('mingyue-s2') - 3);
+---------------------------------------------+
| left('mingyue-s2',length('mingyue-s2') - 3) |
+---------------------------------------------+
| mingyue |
+---------------------------------------------+
1 row in set (0.00 sec)