WebMay 19, 2015 · However illogical it may seem, converting an empty string to other data types produces arbitrary values. This code: SELECT CONVERT (int, '') SELECT CONVERT (float, '') SELECT CONVERT (date, '') SELECT CONVERT (datetime, '') Produces this output: 0 0 1900-01-01 1900-01-01 00:00:00.000. You could expect then that this behavior is consistent ... WebFeb 18, 2024 · 1、问题mysql中在设置主键(id)的默认值时,有一下两种情况:当 id 为 int 类型时,可以直接在创建表时设置id为 id primary key auto_increase,即默认 id 为主键自增长。当 id 为 varchar 类型时,要设置主键id的唯一默认字符串的值,需要使用UUID()函数,但是mysql中不支持默认值为函数,本文就是为了解决这个 ...
MySQL字段默认值设置详解 - MySQL技术 - 博客园
WebNov 11, 2024 · In MySQL, while creating a table, I'like to have empty string '' as value for all needed columns instead of 'NULL'. Is it possible, is it safe and how can I do to do that at … WebFeb 9, 2024 · An empty string is useful when the data comes from multiple resources. NULL is used when some fields are optional, and the data is unknown. Conclusion. A string refers to a character's sequence. Sometimes strings can be empty or NULL. The difference is that NULL is used to refer to nothing. However, an empty string is used to point to a unique ... caddyshack best scenes
Mysql的NULL和Empty String - realcp1018 - 博客园
WebApr 26, 2024 · 在MySQL中NULL值和空字符''是不一样的,这点可能会引起很多新人的困惑,因此查询官网相关的页面总结如下:. 两者的查询方式不一样:NULL值查询使用is … WebJul 30, 2024 · To check the field is empty like ‘ ’or is null, you need to use the IS NULL property or something else. You can check all the conditions with CASE statement. The syntax is as follows: SELECT *, CASE WHEN yourColumnName =’ ‘ THEN ‘yourMessage1’ WHEN yourColumnName IS NULL THEN ‘yourMessage2’ ELSE CONCAT … WebApr 1, 2024 · 建议不要使用NULL或空值,String类型的字段可以设置默认为Empty String(即空字符串’’),Int类型的字段可以设置默认为0。 尤其是使用php做接口开发时,设置字段类型为not null可以避免产生很多问题,如果查询出null数据直接返回给Android或IOS,而移动端又 … cmake install directory 通配符