MySQL按首字母查询

DELIMITER $$  
  
CREATE  
    /*[DEFINER = { user | CURRENT_USER }]*/  
    FUNCTION `401_exam`.`GET_FIRST_PINYIN_CHAR`(PARAM VARCHAR(255))RETURNS VARCHAR(2) CHARSET utf8    
      
    BEGIN  
 DECLARE V_RETURN VARCHAR(255);  
    DECLARE V_FIRST_CHAR VARCHAR(2);  
    SET V_FIRST_CHAR = UPPER(LEFT(PARAM,1));  
    SET V_RETURN = V_FIRST_CHAR;  
    IF LENGTH( V_FIRST_CHAR) <> CHARACTER_LENGTH( V_FIRST_CHAR ) THEN  
    SET V_RETURN = ELT(INTERVAL(CONV(HEX(LEFT(CONVERT(PARAM USING gbk),1)),16,10),  
        0xB0A1,0xB0C5,0xB2C1,0xB4EE,0xB6EA,0xB7A2,0xB8C1,0xB9FE,0xBBF7,  
        0xBFA6,0xC0AC,0xC2E8,0xC4C3,0xC5B6,0xC5BE,0xC6DA,0xC8BB,  
        0xC8F6,0xCBFA,0xCDDA,0xCEF4,0xD1B9,0xD4D1),  
    'A','B','C','D','E','F','G','H','J','K','L','M','N','O','P','Q','R','S','T','W','X','Y','Z');  
    END IF;  
    RETURN V_RETURN;  
    END$$  
  
  
DELIMITER ;  

用到的函数:

left(str,length):从左边开始截取字符串

upper:将字符串转为大写

length(str):计算字符串长度,一个汉字算三个字符,一个数字或字母算一个字符

character_length(str)：汉字、数字、字母都算一个字符
convert(expr USING encode)：不同字符集之间的数据转换
hex(Number or Str)：将数字或字符串转换为十六进制
conv(Number, from, to)：将数字从原来的进制转换成指定的进制
interval(N,N1,N2,N3,......)：将N的值与后面的值列表进行比较

查询SQL：

SELECT a.dev_id,a.dev_name,GET_FIRST_PINYIN_CHAR(a.dev_name) FROM tn_facility a
WHERE  GET_FIRST_PINYIN_CHAR(a.dev_name)='c'