mysql - 创建mysql函数

Question

我想使用以下查询创建一个函数，但发生错误

DELIMITER $$
CREATE FUNCTION getOnlineUserTraffic (x1 VARCHAR(32)) 
RETURNS FLOAT
DETERMINISTIC
BEGIN 
  DECLARE dist FLOAT;
  SET dist = SELECT UsedCreditTraffic FROM uonlineuser WHERE UserName=x1
  RETURN dist;
END$$
DELIMITER ;

//userName= 字符，长度=32

//UsedCreditTraffic = float

Answer 1

尝试:

DELIMITER $$

DROP FUNCTION IF EXISTS getOnlineUserTraffic$$

CREATE FUNCTION getOnlineUserTraffic(x1 VARCHAR(32)) 
RETURNS FLOAT
DETERMINISTIC
BEGIN 
  DECLARE dist FLOAT;
  SET dist = (SELECT UsedCreditTraffic FROM uonlineuser WHERE UserName=x1);
  RETURN dist;
END$$

DELIMITER ;

SQL Fiddle demo