目录前言一、ifnull函数二、nullif函数三、if函数四、if语句（多用于存储过程）五、if-else语句（多用于存储过程）六、if-elseif-else语句（多用于存储过程）总结前言
I\'ve been writing Windows Services for a while and they always seem to work fine for things that开发者_开发问答 need to run every day, few times a week, once a month, etc. but I\'ve been lately think
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