MySQL 使用一个 Insert 语句而不是游标循环

Question

我有这个触发器，它运行良好，但我读到使用游标和循环对性能不利。

那么我怎样才能用一个插入语句代替使用游标和循环，就像更新部分中的那个语句：

CREATE TRIGGER `after_insert_invoice` AFTER INSERT ON `invoicetbl`
 FOR EACH ROW BEGIN
  DECLARE v_finished INTEGER DEFAULT 0;
  DECLARE my_hour INT(11) DEFAULT 0;
  DECLARE my_day INT(11) DEFAULT 0;
  DECLARE my_month INT(11) DEFAULT 0;
  DECLARE current_item_id BINARY(16);
  DECLARE current_item_total_price DECIMAL(11, 2);
  DECLARE current_item_count DECIMAL(11, 3);

  DECLARE cur CURSOR FOR     SELECT  item_id, item_total_price, item_count
        FROM  invoice_itemtbl
        WHERE  invoice_id = NEW.invoice_id;

  DECLARE CONTINUE HANDLER FOR NOT FOUND SET v_finished = 1;

  SET my_month = EXTRACT(YEAR_MONTH FROM NEW.invoice_date);
  SET my_day = CONCAT(my_month, LPAD(DAY(NEW.invoice_date), 2, '0'));
  SET my_hour = CONCAT(my_day, LPAD(HOUR(NEW.invoice_date), 2, '0'));

  IF NEW.invoice_type = 0 THEN

        OPEN cur;

        start_loop: LOOP

        FETCH cur INTO current_item_id,
                       current_item_total_price,
                       current_item_count;

        IF v_finished = 1 THEN 
            LEAVE start_loop;
        ELSE

（续...）

        INSERT
          INTO  sales_result_company_item_month(company_id, currency_id,
                time_value, item_id, result, invoices_count, item_qty )
          VALUES  (NEW.company_id, NEW.currency_id, my_month, current_item_id,
                    current_item_total_price, 1, current_item_count )
          ON DUPLICATE KEY 
          UPDATE  result = result + current_item_total_price,
                  invoices_count = invoices_count + 1,
                  item_qty = item_qty + current_item_count;

        END IF;
        END LOOP;

      CLOSE cur;

  END IF;

  IF NEW.invoice_type = 1 THEN

    //like here:
    UPDATE  sales_result_company_item_month m
    INNER JOIN  
    (
        SELECT  item_id, returns_count, returns_total
            FROM  invoice_returns
            WHERE  return_invoice_id = NEW.invoice_id
    ) f  ON m.item_id = f.item_id SET m.result = m.result - f.returns_total,
        m.item_qty = m.item_qty - f.returns_count
    WHERE  m.company_id = NEW.company_id
      AND  m.currency_id = NEW.currency_id
      AND  m.time_value = my_month;

  END IF;

END

（从评论中复制——在 'fixing' 问题之后，包括 Cursor 的消除）：

INSERT
     INTO  sales_result_company_item_month
         (company_id, currency_id, time_value, item_id,
          result, invoices_count, item_qty) 
SELECT  NEW.company_id, NEW.currency_id, my_month, t.item_id,
        t.item_total_price, 1, t.item_count
    FROM  invoice_itemtbl t
    WHERE  invoice_id = NEW.invoice_id
    ON DUPLICATE KEY UPDATE 
        result = result + t.item_total_price,
        invoices_count = invoices_count + 1,
        item_qty = item_qty + t.item_count;

Answer 1

是的，您或许可以去掉 Cursor。

可以做到

INSERT INTO t ( ... )
    ON DUPLICATE KEY UPDATE ...
    SELECT ...;

其中，SELECT 将所有行提取到 "upsert"。您可能需要 UPDATE 子句中的 VALUES() 来区分所选列和 table 中已有的列。请参阅手册中的示例。

如果您想进一步讨论这个问题，请

为相关的table提供SHOW CREATE TABLE，
摆脱 kruft（例如，my_day，未使用）
用 _ 前缀局部变量，或以其他方式将它们与 table 列区分开来。

current_item_count DECIMAL(11, 3)不解：什么"count"需要3位小数？

MySQL 使用一个 Insert 语句而不是游标循环

MySQL use one Insert statement instead of cursor loop

mysql

performance

cursor

insert-into