mysql - MySQL 用户定义函数——Haversine 公式

Question

我有以下代码：

CREATE FUNCTION CalculateDistance
    (`Code1` VARCHAR(8), `Code2` VARCHAR(8)) RETURNS FLOAT
BEGIN
    DECLARE Code1Lat FLOAT;
    DECLARE Code1Long FLOAT;
    DECLARE Code2Lat FLOAT;
    DECLARE Code2Long FLOAT;
    DECLARE DLat FLOAT;
    DECLARE DLong FLOAT;
    DECLARE A FLOAT;
    DECLARE C FLOAT;
    Code1Lat = SELECT `lat` FROM `vb_postcodes` WHERE `code` LIKE Code1;
    Code1Long = SELECT `lng` FROM `vb_postcodes` WHERE `code` LIKE Code1;
    Code2Lat = SELECT `lat` FROM `vb_postcodes` WHERE `code` LIKE Code2;
    Code2Long = SELECT `lng` FROM `vb_postcodes` WHERE `code` LIKE Code2;
    DLat = (Code2Lat - Code1Lat) * PI() / 180;
    DLong = (Code2Long - Code1Long) * PI() / 180;
    Code1Lat = Code1Lat * PI() / 180;
    Code2Lat = Code2Lat * PI() / 180;
    A = (SIN(DLat / 2) * SIN(DLat / 2)) + (SIN(DLong / 2) * SIN(DLong / 2)) * COS(Lat1)    * COS(Lat2);
    C = 2 * ATAN2(SQRT(A), SQRT(1 - A));
    Return (3960 * C);
END

这是计算两个坐标之间距离的半正弦公式。坐标存储在vb_postcodes具有以下属性的表中：code、lng 和 lat。当我尝试执行代码时，出现语法错误。

请原谅我的问题，这是我第一次制作用户定义的函数。