MySQL,stored-function,使用STRING变量作为QUERY

Question

我想知道是否有可能在mysql存储函数或存储过程中将mysql查询组成一个字符串变量,以后可以执行？我有一个get_district_part ((district_id INT,county_id INT,city_id INT,zip_id INT)) RETURNS INT引用该表的存储函数:

CREATE TABLE IF NOT EXISTS `modx`.covereage_district_part(
    id      INT     NOT NULL    AUTO_INCREMENT  PRIMARY KEY,
    districtID  INT     NOT NULL,
    countyID    INT,
    cityID      INT,
    zipID       INT,
    FOREIGN KEY (districtID) REFERENCES `modx`.coverage_district (id),
    FOREIGN KEY (countyID) REFERENCES `modx`.coverage_county (id),
    FOREIGN KEY (cityID) REFERENCES `modx`.coverage_city (id),
    FOREIGN KEY (zipID) REFERENCES `modx`.coverage_zip (id)
);

get_distrct_part意味着返回行mathing的ID district_id及的某种组合county_id,city_id和zip_id.问题是我想返回与id的确切组合匹配的行的id,而不是包含任何这些想法的行的id.为此,我想要分割我的查询语句,以便它是专门为所提供的ID构建的.如果可以,我试图不必匹配空值.

我意识到这可以很容易地用PHP完成,但我想这样做作为mysql存储过程,如果我可以没有其他原因,那么所有其他功能都是存储过程.

Answer 1

是的,你可以PREPARE和EXECUTE一个字符串作为存储过程的动态SQL.

delimiter //
CREATE PROCEDURE get_district_part (district_id INT, county_id INT, city_id INT, zip_id INT)
BEGIN
  SET @query = 'SELECT id FROM covereage_district_part WHERE 1=1';

  IF (district_id IS NOT NULL) THEN
    SET @query = CONCAT(@query, ' AND districtID=', district_id);
  END IF;

  IF (county_id IS NOT NULL) THEN
    SET @query = CONCAT(@query, ' AND countyID=', county_id);
  END IF;

  IF (city_id IS NOT NULL) THEN
    SET @query = CONCAT(@query, ' AND cityID=', city_id);
  END IF;

  IF (zip_id IS NOT NULL) THEN
    SET @query = CONCAT(@query, ' AND zipID=', zip_id);
  END IF;

  PREPARE stmt1 FROM @query;

  EXECUTE stmt1;
END //
delimiter ;

call get_district_part(1,1,1,1);
call get_district_part(1,1,null,null);

注意:但是,您无法在存储的函数中执行动态SQL.您的问题提到RETURNS使用一个存储函数的子句来声明您的例程.