How Do I Use Dynamic Variable Assignment in MySQL?

Detailed explanation of MySQL dynamic variable assignment

MySQL variables are used to store temporary values ​​used in queries and are crucial in database operations. The variable declaration method depends on the variable type.

User-defined variables

Starts with "@" and can be used without declaration or initialization. They can store a variety of data types, including NULL, and can be assigned using SET or SELECT statements.

Local variables

When used in a stored procedure, the DECLARE statement must be used. The scope is limited to the BEGIN...END block, and the initial value is NULL unless an initial value is specified using DEFAULT.

Server system variables

Begins with "@@", indicating the server's configuration settings. Can be a global variable (affects the entire server) or a session variable (affects a single client connection). Use SHOW VARIABLES or SELECT @@var_name to see the current value. These variables can be dynamically modified using SET GLOBAL or SET SESSION.

START and FINISH variable examples

The following example demonstrates how to perform a query using user-defined variables:

SET @start = 1;
SET @finish = 10;

SELECT * FROM places WHERE place BETWEEN @start AND @finish;

Please note that the scope of user-defined variables is session-specific and is only visible within the current client connection.

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