mysql sql变量

-- 声明和使用用户定义变量
SET @myVariable = 10;
SELECT @myVariable;

-- 使用会话变量
SET @@global.max_connections = 200;
SELECT @@global.max_connections;

-- 在存储过程中使用变量
DELIMITER //
CREATE PROCEDURE GetEmployee(IN empID INT)
BEGIN
    DECLARE empName VARCHAR(255);
    SELECT name INTO empName FROM employees WHERE id = empID;
    SELECT empName;
END //
DELIMITER ;

CALL GetEmployee(1);

SET @myVariable = 0; -- 初始化变量

DELIMITER //
CREATE PROCEDURE MyProcedure()
BEGIN
    DECLARE localVariable INT;
    SET localVariable = 10;
    SELECT localVariable;
END //
DELIMITER ;

SET @myVariable = '10'; -- 字符串类型的'10'
SELECT CAST(@myVariable AS UNSIGNED); -- 转换为无符号整数