开发同事反映MySQL创建自定义函数时报错：
CREATE DEFINER = CURRENT_USER FUNCTION `ISBLANK`(`s` varchar)
RETURNS int(1)
BEGIN
RETURN ISNULL(s) or LENGTH(TRIM(s))=0;
END;
报错如下：
[SQL]CREATE DEFINER = CURRENT_USER FUNCTION
ISBLANK(svarchar)
RETURNS int(1)
BEGIN
RETURN ISNULL(s) or LENGTH(TRIM(s))=0;
[Err] 1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘)
RETURNS int(1)
BEGIN
RETURN ISNULL(s) or LENGTH(TRIM(s))=0’ at line 1
原因：未定义VARCHAR长度，VARCHAR没有默认长度，未声明就会报错，修改一下就OK了：
CREATE DEFINER = CURRENT_USER FUNCTION `ISBLANK`(`s` varchar(20))
RETURNS int(1)
BEGIN
RETURN ISNULL(s) or LENGTH(TRIM(s))=0;
END;
PS：char可以不定义长度使用，默认长度是1。