CHAR_LENGTH(str)
返回值為字串str 的長度，長度的單位為字元。一個多位元組字元算作一個單字元。
+------------------------+
| CHAR_LENGTH(`klvchen`) |
+------------------------+
| 7 |
+------------------------+
1 row in set (0.00 sec)
mysql> SELECT CHAR_LENGTH(`你`);
+--------------------+
| CHAR_LENGTH(`你`) |
+--------------------+
| 1 |
+--------------------+
1 row in set (0.00 sec)CONCAT(str1,str2,…)
字串拼接, 如有任何一個引數為NULL ，則返回值為 NULL。
mysql> SELECT CONCAT(`kl`,`v`,`chen`);
+-------------------------+
| CONCAT(`kl`,`v`,`chen`) |
+-------------------------+
| klvchen |
+-------------------------+
1 row in set (0.00 sec)CONCAT_WS(separator,str1,str2,…)
字串拼接（自定義連線符）CONCAT_WS()不會忽略任何空字串。 (然而會忽略所有的 NULL）
mysql> SELECT CONCAT_WS(`_`,`chen`,`wj`);
+----------------------------+
| CONCAT_WS(`_`,`chen`,`wj`) |
+----------------------------+
| chen_wj |
+----------------------------+
1 row in set (0.01 sec)
mysql> SELECT CONCAT_WS(`_`,`chen`,` wj `, NULL, `hehe`);
+--------------------------------------------+
| CONCAT_WS(`_`,`chen`,` wj `, NULL, `hehe`) |
+--------------------------------------------+
| chen_ wj _hehe |
+--------------------------------------------+
1 row in set (0.00 sec)CONV(N,from_base,to_base)
進位制轉換
mysql> SELECT CONV(`a`,16,2);
+----------------+
| CONV(`a`,16,2) |
+----------------+
| 1010 |
+----------------+
1 row in set (0.00 sec)FORMAT(X,D)
將數字X 的格式寫為`#,###,###.##`,以四捨五入的方式保留小數點後 D 位， 並將結果以字串的形式返回。若 D 為 0, 則返回結果不帶有小數點，或不含小數部分。
mysql> SELECT FORMAT(1.23,4);
+----------------+
| FORMAT(1.23,4) |
+----------------+
| 1.2300 |
+----------------+
1 row in set (0.00 sec)INSERT(str,pos,len,newstr)
str 原字串; pos 要替換位置其實位置(從1開始); len：替換的長度；newstr：需要替換的符串
簡潔概況為：先從 pos 處刪除 len 長度的字串，再由新的字串代替
mysql> SELECT INSERT(`klvchen`, 1, 1, `j`);
+------------------------------+
| INSERT(`klvchen`, 1, 1, `j`) |
+------------------------------+
| jlvchen |
+------------------------------+
1 row in set (0.00 sec)
mysql> SELECT INSERT(`klvchen`, 1, 1, `ja`);
+-------------------------------+
| INSERT(`klvchen`, 1, 1, `ja`) |
+-------------------------------+
| jalvchen |
+-------------------------------+
1 row in set (0.00 sec)
mysql> SELECT INSERT(`klvchen`, 1, 2, `a`);
+------------------------------+
| INSERT(`klvchen`, 1, 2, `a`) |
+------------------------------+
| avchen |
+------------------------------+
1 row in set (0.00 sec)INSTR(str,substr)
返回字串 str 中子字串的第一個出現位置。
mysql> SELECT INSTR(`klvchen`,`l`);
+----------------------+
| INSTR(`klvchen`,`l`) |
+----------------------+
| 2 |
+----------------------+
1 row in set (0.00 sec)LOCATE(substr,str,pos)
獲取子序列索引位置
mysql> SELECT LOCATE(`l`,`klvchen`,1);
+-------------------------+
| LOCATE(`l`,`klvchen`,1) |
+-------------------------+
| 2 |
+-------------------------+
1 row in set (0.01 sec)LEFT(str,len)
返回字串 str 從開始的 len 位置的子序列字元。
mysql> SELECT LEFT(`klvchen`,2);
+-------------------+
| LEFT(`klvchen`,2) |
+-------------------+
| kl |
+-------------------+
1 row in set (0.00 sec)RIGHT(str,len)
從字串 str 開始，返回從後邊開始 len個字元組成的子序列
mysql> SELECT RIGHT(`klvchen`, 2);
+---------------------+
| RIGHT(`klvchen`, 2) |
+---------------------+
| en |
+---------------------+
1 row in set (0.00 sec)LOWER(str)
字串轉化為小寫
mysql> SELECT LOWER(`KLVCHEN`);
+------------------+
| LOWER(`KLVCHEN`) |
+------------------+
| klvchen |
+------------------+
1 row in set (0.00 sec)UPPER(str)
字串轉化為大寫
mysql> SELECT UPPER(`klvchen`);
+------------------+
| UPPER(`klvchen`) |
+------------------+
| KLVCHEN |
+------------------+
1 row in set (0.00 sec)LTRIM(str)
返回字串 str ，左邊的空格字元被刪除。
mysql> SELECT LTRIM(` klvchen`);
+--------------------+
| LTRIM(` klvchen`) |
+--------------------+
| klvchen |
+--------------------+
1 row in set (0.00 sec)RTRIM(str)
返回字串 str ，結尾空格字元被被刪除。
mysql> SELECT RTRIM(`klvchen `);
+----------------------+
| RTRIM(`klvchen `) |
+----------------------+
| klvchen |
+----------------------+
1 row in set (0.00 sec)TRIM([{BOTH | LEADING | TRAILING} [remstr] FROM] str) TRIM(remstr FROM] str)
返回字串 str ， 其中所有remstr 字首和/或字尾都已被刪除。若分類符BOTH、LEADIN或TRAILING中沒有一個是給定的,則假設為BOTH 。 remstr 為可選項，在未指定情況下，可刪除空格。
mysql> SELECT TRIM(` kl `);
+------------------+
| TRIM(` kl `) |
+------------------+
| kl |
+------------------+
1 row in set (0.00 sec)
mysql> SELECT TRIM(LEADING `x` FROM `xxklxx`);
+----------------------------------+
| TRIM(LEADING `x` FROM `xxklxx`) |
+----------------------------------+
| klxx |
+----------------------------------+
1 row in set (0.00 sec)
mysql> SELECT TRIM(BOTH `x` FROM `xxklxx`);
+-------------------------------+
| TRIM(BOTH `x` FROM `xxklxx`) |
+-------------------------------+
| kl |
+-------------------------------+
1 row in set (0.00 sec)
mysql> SELECT TRIM(trailing `x` FROM `xxklxx`);
+-----------------------------------+
| TRIM(trailing `x` FROM `xxklxx`) |
+-----------------------------------+
| xxkl |
+-----------------------------------+
1 row in set (0.00 sec)REPEAT(str,count)
返回一個由重複的字串 str 組成的字串，字串str重複的次數等於count的值 。
若 count <= 0,則返回一個空字串；若str 或 count 為 NULL，則返回 NULL 。
mysql> SELECT REPEAT(`ha`,3);
+----------------+
| REPEAT(`ha`,3) |
+----------------+
| hahaha |
+----------------+
1 row in set (0.00 sec)REPLACE(str,from_str,to_str)
返回字串str 以及所有被字串to_str替代的字串from_str 。
mysql> SELECT REPLACE(`klvchel`, `l`, `i`);
+------------------------------+
| REPLACE(`klvchel`, `l`, `i`) |
+------------------------------+
| kivchei |
+------------------------------+
1 row in set (0.00 sec)REVERSE(str)
返回字串 str ，順序和字元順序相反。
mysql> SELECT REVERSE(`klvchen`);
+--------------------+
| REVERSE(`klvchen`) |
+--------------------+
| nehcvlk |
+--------------------+
1 row in set (0.00 sec)SUBSTRING(str,pos,len)
獲取字串子序列
mysql> SELECT SUBSTRING(`klvchen`, 1, 3);
+----------------------------+
| SUBSTRING(`klvchen`, 1, 3) |
+----------------------------+
| klv |
+----------------------------+
1 row in set (0.00 sec)
mysql> SELECT SUBSTRING(`klvchen`, 3);
+-------------------------+
| SUBSTRING(`klvchen`, 3) |
+-------------------------+
| vchen |
+-------------------------+
1 row in set (0.00 sec)
mysql> SELECT SUBSTRING(`klvchen` FROM 3);
+-----------------------------+
| SUBSTRING(`klvchen` FROM 3) |
+-----------------------------+
| vchen |
+-----------------------------+
1 row in set (0.00 sec)
mysql> SELECT SUBSTRING(`klvchen`, -3);
+--------------------------+
| SUBSTRING(`klvchen`, -3) |
+--------------------------+
| hen |
+--------------------------+
1 row in set (0.00 sec)
mysql> SELECT SUBSTRING(`klvchen`, -3, 2);
+-----------------------------+
| SUBSTRING(`klvchen`, -3, 2) |
+-----------------------------+
| he |
+-----------------------------+
1 row in set (0.00 sec)
mysql> SELECT SUBSTRING(`klvchen` FROM -3 FOR 2);
+------------------------------------+
| SUBSTRING(`klvchen` FROM -3 FOR 2) |
+------------------------------------+
| he |
+------------------------------------+
1 row in set (0.01 sec)