错误：sql="select * from itlogger where it=null"
sql="select * from itlogger where it='' "
sql="select * from itlogger where len(it)=0"
正确：sql="select * from itlogger where it is null"
sql="select * from itlogger where it='' "
sql="select * from itlogger where len(it)=0"
正确：sql="select * from itlogger where it is null"
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用if 语句判断字段是否为空时,为什么用it=" "判断时，结论为错误的，而用it<>" "却能做出正确的判断呢？
我的理解，真正空为null,而null<>"",所以判断null=""时错误，null<>""时正确！