问题描述：MySQL进行字符串比较时发生错误：

SELECT  
    a.equ_no,  
    b.fullCode  
FROM  
    equipment a,  
    (  
        SELECT  
            t.*, getEquTypeFullCode (t.equType_id) AS fullCode  
        FROM  
            equ_type t  
    ) b  
WHERE  
    substring(a.equ_no, 1, 5) = b.fullCode  

错误如下：

[Err] 1267 - Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (utf8_general_ci,IMPLICIT) for operation '='  

解决方法：将比较等式一边进行字符串转换，如改为“CONVERT(x USING utf8) COLLATE utf8_unicode_ci”,b.fullCode 为你的变量

SELECT  
    a.equ_no,  
    b.fullCode  
FROM  
    equipment a,  
    (  
        SELECT  
            t.*, getEquTypeFullCode (t.equType_id) AS fullCode  
        FROM  
            equ_type t  
    ) b  
WHERE  
    substring(a.equ_no, 1, 5) = CONVERT(b.fullCode USING utf8) COLLATE utf8_unicode_ci;