MySQL，最好插入NULL或空字符串? [英] MySQL, better to insert NULL or empty string?

问题描述

我在一个网站上有一个表格，其中包含很多不同的字段.一些字段是可选的，而某些字段是必填的.在我的数据库中，我有一个包含所有这些值的表，是否将NULL值或空字符串插入用户未放置任何数据的数据库列中是更好的做法?

I have a form on a website which has a lot of different fields. Some of the fields are optional while some are mandatory. In my DB I have a table which holds all these values, is it better practice to insert a NULL value or an empty string into the DB columns where the user didn't put any data?

推荐答案

通过使用NULL，您可以区分不输入数据"和不输入数据".

By using NULL you can distinguish between "put no data" and "put empty data".

更多区别:

• NULL的LENGTH是NULL，空字符串的LENGTH是0.

• A LENGTH of NULL is NULL, a LENGTH of an empty string is 0.

NULL s在空字符串之前排序.

NULLs are sorted before the empty strings.

COUNT(message)将计算空字符串，但不计算NULL s

COUNT(message) will count empty strings but not NULLs

您可以使用绑定变量搜索空字符串，但不能搜索NULL.此查询:

You can search for an empty string using a bound variable but not for a NULL. This query:

SELECT  *
FROM    mytable 
WHERE   mytext = ?

无论您从客户端传递什么值，

都永远不会匹配mytext中的NULL.要匹配NULL，您必须使用其他查询:

will never match a NULL in mytext, whatever value you pass from the client. To match NULLs, you'll have to use other query:

SELECT  *
FROM    mytable 
WHERE   mytext IS NULL

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