1, today, an interesting thing happened, data transmission is greater than the standard length of a given field, I cranked up the field length, data transmission over. Who knows, other people's data does not meet the standard, you want to delete the re-engage, then you how long it deleted data, or the query data out long.
A: spoilers about, in fact, use char_length () check out, you can put these deleted, and then turn up field length of a little tune on the line. Note, I practice fields are Chinese characters Ha, do not write a tutorial written murder.
2, first look, Mysql in length (), char_length () difference.
1), length (): mysql inside the length () function is used to obtain a built-in function of the length of the string.
2), char_length (): See string length in mysql there is also a built-in function is a function char_length ().
3), the difference between these two functions is:
a), length (): in bytes, the encoding utf8, three bytes of a character, a number or letter one byte. Under gbk coding, two bytes of a character, a number or letter one byte.
b), char_length (): units of characters, either letters or numbers or characters are regarded as a character.
3, extend it, varchar type of change after MySQL5.0.3 version.
1）、MySQL 5.0.3 之前：0--255字节，如：varchar(20)中的20表示字节数，如果存放utf-8编码的话只能放6个汉字。varchar(n)，这里的n表示字节数。
MySQL 5.0.3 之后：0--65535字节，varchar(20)表示字符数，不管什么编码，既汉字也能放20个。但最多占65532字节（两个字节存放长度，小于255字节用1个字节存放长度），varchar(n)这里的n表示字符数，比如varchar（200），不管是英文还是中文都可以存放200个。其他具体区别，可自行网上查询。
4、length()<>char_length()，可以用来检验是否含有中文字符。
utf-8编码中判定某个字段为全英文，length(字段) = char_length(字段)即可。