mysql如何过滤特殊字符？用PHP语言。高分求助，给补分

function deletehtml($str) {

$str = trim($str)

$str = preg_replace("</P>","1234a3211",$str)

$str = preg_replace("</p>","1234a3211",$str)

$str = preg_replace("<br/>","1234a3211",$str)

$str = preg_replace("/<(.[^>]*)>/","",$str)

$str = preg_replace("/([\r\n])[\s]+/","",$str)

$str = preg_replace("/-->/","",$str)

$str = preg_replace("/<!--.*/","",$str)

$str = preg_replace("/&(quot|#34)/","",$str)

$str = preg_replace("/&(amp|#38)/", "/&/",$str)

$str = preg_replace("/&(lt|#60)/", "/</",$str)

$str = preg_replace("/&(gt|#62)/", ">",$str)

$str = preg_replace("/&(nbsp|#160)/", "",$str)

$str = preg_replace("/&(iexcl|#161)/", "/\xa1/",$str)

$str = preg_replace("/&(cent|#162)/", "/\xa2/",$str)

$str = preg_replace("/&(pound|#163)/", "/\xa3/",$str)

$str = preg_replace("/&(copy|#169)/", "/\xa9/",$str)

$str = preg_replace("/(\d+)/", "",$str)

$str = preg_replace("/</", "",$str)

$str = preg_replace("/>/", "",$str)

$str = preg_replace("/\r\n/", "",$str)

$str = preg_replace("/1234a3211/", "/<br/>/",$str)

return $str

}

select

distinct可以去掉重复记录。

disctinct将重复的记录忽略，但它忽略的是完全一致的重复记录，而不是其中某个字段重复的记录，或者说，distinct查询一个字段时好使，多个字段就不好使。

所以用聚合函数和group

by实现

注意：group

by只能跟聚合函数搭配使用

例表

ID

username

password

TRDESC

1

A

abcdef

QR

2

A

abcdef

W34

3

A

bbbbbb

AD

4

B

aaaaaa

asdf

查询username和password组合起来的条件不能重复的查询结果(这个都能重复，不能不说这是个烂摊子)

select

*

from

mytable

where

ID

in(select

max(ID)

from

mytable

group

by

username,password)

当username和password重复时，取ID最小的记录：

select

*

from

mytable

where

ID

in(select

min(ID)

from

mytable

a

group

by

username,password)

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