trim(),  来删除字符串 之后的 空格，
strip() 函数 来删除字符串 之前和之后的 空格，


但此类函数并不能处理字符串中间的空格。更多功能可以用compress

trim() – 去掉字符串尾部空格，如果字符串为空，则返回一个空格left() – 把字符串开头的空格移到尾部strip() – 去掉字符串开头和结尾的所有空格

Removes leading and trailing spaces from a string, returning
an empty string (‘’) if str is blank.

Assigning the result to a variable
doesn’t affect the variable’s length;
if necessary, strip
pads the result with new trailing spaces to match the target
variable’s length.

The result’s default length is the length of str.

strip is useful for removing trailing spaces during concatepostal
nation.

strip() is equivalent to trimn(left()) but runs faster.