创建自定义MySQL功能？

Question

我刚开始使用MySQL和PHP,我想知道是否可以创建自定义函数.这段代码片段应该说明我正在尝试做什么.

// a somewhat complicated formula not suitable to embed into the query
function Distance($latA, $lonA, $latB, $lonB)
{
  // earth's radius
  $radius = 3956;

  $latA = deg2rad($latA);
  $lonA = deg2rad($lonA);
  $latB = deg2rad($latB);
  $lonB = deg2rad($lonB);

  // calculate deltas
  $deltaLat = $latB - $latA;
  $deltaLon = $lonB - $lonA;

  // calculate Great Circle distance
  $result = pow(sin($deltaLatitude / 2.0), 2) + (cos($latA) * cos($latB) * pow(sin($deltaLon / 2.0), 2));
  $distance = $radius * 2 * atan2(sqrt($result), sqrt(1 - $result));

  return $distance;
}

// how can I call Distance() in my query?
$query = "SELECT lat, lon FROM zipcodes WHERE Distance(lat, lon, 0, 0) < 20";
mysql_query($query);

在此先感谢您的帮助!

Answer 1

您在应用程序中声明此MySQL函数,它将保留在数据库中,直到重新启动数据库服务器.

mysql_query("CREATE FUNCTION Distance(LAT_A INT, LON_A INT, LAT_B INT, LON_B INT, )
RETURNS INT
READS SQL DATA
DETERMINISTIC
BEGIN
DECLARE radius, deltaLat, deltaLon, result, distance BIGINT;
SET radius=3956;
SET deltaLat=LAT_B-LAT_A;
SET deltaLon=LON_B-LON_A;
SET result=POW(SIN(deltaLat/2), 2) + (COS(LAT_A) * COS(LAT_B) * POW(SIN(deltaLon/2.0), 2));
SET distance=radius * 2 * ATAN2(SQRT(result), SQRT(1 - result));
RETURN distance;
END");

这使用MySQL的数学函数.将此处理卸载到数据库是快速有效的(数据不必通过网络传输,并且您只返回所需的结果).

一旦你宣布了这个,就可以这样使用它:

$query = "SELECT lat, lon FROM zipcodes WHERE Distance(lat, lon, 0, 0) < 20";
mysql_query($query);

但是,如果数据库重新启动,则先前声明的任何函数或过程都将丢失.可以Function functionName does not exist在应用程序级别正常处理MySQL错误1305().

在您的数据库错误处理程序

switch (mysql_errno()):
    case 1305:
        if (false === $database->_declareStoredProcedureFlag) {
             if ($c = preg_match_all("/FUNCTION [a-zA-Z0-9]+\." .
                 "([a-zA-Z0-9_]*) does not exist/is",
                 mysql_error(), $matches)
             ) {
                 $storedFunctionName = $matches[1][0];
                 $database->_declareStoredProcedureFlag = true;
                 if (true === $database->declareStoredFunction($storedFunctionName)) {
                     $result = mysql_query($query);
                 }
             }
         }
         break;
    ...