mysql if variable null

Add by Zhj: In the MySQL5.6 of some parameters have been increased, see http://dev.mysql.com/doc/refman/5.6/en/server-system-variables.htmlOriginal: http://mageedu.blog.51cto.com/4265610/1062628Marco Education Linux operation and maintenance

MySQL has become one of the most widely used databases on the network, especially for Web applications. it occupies the absolute advantage of small and medium applications. All of this comes from its small and easy-to-use, secure and effective, open

In MySQL, the processing of NULL fields, it is important to note that when there is null in the processing query condition, it is possible that the value you get is not desired because, in MySQL, the null value equals (=) is judged equal (=) or

Server system Variables (System variable)The MySQL system variable (systems variables) refers to the various system variables of the MySQL instance, which are actually some system parameters that are used to initialize or set the database to occupy

1. download MySql 1. download MySql Open http://www.mysql.com/downloads/mysql/#downloads download in browser My downloaded version is Red Hat 5 version of http://www.mysql.com/downloads/mirror.php? Id = 407552 Upload the file to the server, or

Mysql Procedure parameter is NULL problem analysis bitsCN.com An interesting thing was found during the recent writing process. Mysql procedure has its own unique processing method when passing parameters. For example, if the parameter is defined as

18.2.1 MySQL server has gone away errors related to Lost connection to server during query. The most common cause of the MySQL server has gone away error is that the server times out and closes the connection. By default, if nothing happens, the

In common: case-insensitive, both variables Different points: Global variables are read-only in the system and can be modified in a configuration file Terminology classification for MySQL variables: 1. User variable: Starting with "@" in the form

String function string comparison function if the result length is greater than the maximum value of the max_allowed_packet system variable, the return value of the string value function is NULL. See section 7.5.2 "Adjust server Parameters ". String

Believe that a lot of people who have been using MySQL for a long time, the concept of these two field properties is not very clear, the general will have the following questions: My field type is not NULL, why can I insert a null value