mysql 一排除语句怎么优化。。

select tab.* from tab,(select max(b) b, a from tab group by a) tab_b

where tab.a = tab_b.a and tab.b = tab_b.b

$faxx=$_POST['fax'] as int

$telenum=$_POST['telenum'] as int

修改成这样试试：

$faxx=(int)$_POST['fax'])

$telenum=(int)$_POST['telenum']

可以这样写SQL：

update tableName set colName='' where colName is null

前提是没有约束限制向表字段写入“空字符串”

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