How Do I Declare and Use Variables in MySQL?

Detailed explanation of MySQL variables

MySQL supports multiple types of variables for storing and manipulating data:

User-defined variables

• Starts with "@" symbol.
• Use SET or SELECT statements for assignment.
• Only valid in the current user session.
• Example: SET @变量名 = 值;

Local variables

• does not start with any symbol.
• Must be declared using the DECLARE statement before it can be used.
• Only valid within the scope of a stored procedure or function.
• Example: DECLARE 变量名 数据类型 DEFAULT 值;

Server system variables

• Start with "@@" symbol.
• Set server-wide configuration options.
• Can be modified dynamically using SET GLOBAL or SET SESSION.
• Example: SHOW VARIABLES LIKE '%变量名%'; View current settings.

Code Example

The following code demonstrates the use of user-defined variables:

<code class="language-sql">SET @起始值 = 1, @结束值 = 10;

SELECT * FROM places WHERE place BETWEEN @起始值 AND @结束值;</code>

User-defined variables @起始值 and @结束值 are used here. The SET statement initializes these two variables. The BETWEEN operator filters results where the place column value is within the specified range.

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