Question

我尝试用存储的SQL过程替换使用DB运行多个请求的重型Java方法。它正在开展工作，但我预计会有更高的性能提升。过程的逻辑（以及Java方法）：

从table1（目的）获取ID列表
迭代列表并从table2（记录）获取每个id的字段的平均值
返回列表对id / average_value

程序中是否存在效率问题？

DROP PROCEDURE IF EXISTS test1.getGeneralAverage;
CREATE DEFINER=root@localhost PROCEDURE getGeneralAverage()
  BEGIN
    DECLARE p_id BIGINT(20);
    DECLARE exit_loop BOOLEAN;
    DECLARE cur CURSOR FOR
          SELECT purpose_id FROM purpose
              WHERE purpose.type = 'GENERAL'
                AND (SELECT COUNT(*) > 0 FROM record
                      WHERE record.purpose_id=purpose.purpose_id) is true;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET exit_loop = TRUE;
    CREATE TEMPORARY TABLE IF NOT EXISTS general_average
            (id BIGINT(20), average DOUBLE) ENGINE=memory;
    TRUNCATE TABLE general_average;
    OPEN cur;
    average_loop: LOOP
      FETCH cur INTO p_id;
      INSERT INTO test1.general_average (id, average)
           VALUES (p_id, (SELECT AVG(amount) FROM record
                            WHERE record.purpose_id=p_id));
      IF exit_loop THEN
        CLOSE cur;
        LEAVE average_loop;
      END IF;
    END LOOP average_loop;
    INSERT INTO test1.general_average (id, average)
         VALUES (0,
           (select avg(amount) from record where purpose_type='CUSTOM'));
    SELECT * FROM general_average;
  END

Answer 1

要改变的几种模式......

尽量避免CURSORs;通常，整个操作可以使用单个SQL语句完成。那会更快。
INSERT ... VALUES (0, ( SELECT ... ) ) - ＆gt; INSERT ... SELECT 0, ...
只需提供结果，就不要使用TEMP表。在您的情况下，您可能需要UNION ALL一次交付两个块。

使用游标和临时表时MySQL存储过程性能问题

1 个答案: