MySQL Variables. Variables are used for storing data or information during the execution of a program. It is a way of labeling data with an appropriate name that helps to understand the program more clearly by the reader. The main purpose of the variable is to store data in memory and can be used throughout the program.

Note. The names of some Transact-SQL system functions begin with two at signs (@@). Although in earlier versions of SQL Server, the @@functions are referred to as global variables, @@functions aren't variables, and they don't have the same behaviors as variables.

2018-10-18 · We can declare a variable in MySQL with the help of SELECT and SET command. Before declaring a variable we need to prefix the symbol ‘@’ The syntax is as follows −. SELECT @ yourVariableName; The symbol ‘@’ tells that it is a user defined variable or not. If there is no symbol, that would mean it is a local variable. There are mainly three types of variables in MySQL: User-defined variables (prefixed with @ ): You can access any user-defined variable without declaring it or initializing it. If you refer to a variable that has not been initialized, it has a value of NULL and a type of string.

Mysql variables

Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. In MySQL, you can access user-defined variables without declaring or initializing them previously. If you do so, a NULL value is assigned to the variable when initialized. For example, if you use SELECT with a variable without giving a value to it, as in this case: We can declare a variable in MySQL with the help of SELECT and SET command.

la manière de manipuler les variables, les structures de contrôle comme les avec une base MySQL et les instructions du langage SQL qui sont nécessaires.

The maximum length of the user-defined variable is 64 characters as of MySQL 5.7.5. The user-defined variables are not case-sensitive. It means that the @id and @ID are the same.

SQL variables are a MySQL-specific extension, so they will not work with other database engines. [ 5 ] In MySQL 4, you can use multiple-table DELETE statements to accomplish tasks like this with a single query.

You might get the results you expect, but this is not guaranteed.

User-defined variables are session-specific. That is, a user variable defined by one client cannot be seen or used by other clients. They can be used in SELECT queries using Advanced MySQL user variable techniques. Local Variables (no prefix) : Local variables needs to be declared using DECLARE before accessing it. They can be used as local mysql-ldap_user_variable. When set, sessions will have a variable set with the user_name value, ie: SET @mysql-ldap_user_variable:='username' The use of this variable can be for auditing purposed backend side. For example, if a trigger on a table will use that session variable.
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Before MySQL 5.0, user variable names are case-sensitive.

2017-07-06 · In MySQL they are called variables, and it’s very easy to see the current values.
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Log into your MySQL database and type: · You will see the following: · mysql> show variables;.

It provides simple examples for clarity. User-variables names are case insensitive, though they were case sensitive in MySQL 4.1 and older versions.