Question

如何将以下程序转换为MySQL格式？

这是要转换的作品：

DECLARE @CurrentFirstName varchar(300)
DECLARE @CurrentAge INT

DECLARE CursorName CURSOR FAST_FORWARD FOR 
    SELECT Firstname,Age 
    FROM Customers

OPEN CursorName
FETCH NEXT FROM CursorName INTO @CurrentFirstName, @CurrentAge

WHILE @@FETCH_STATUS = 0
BEGIN
      IF @AGE>60 /*this is stupid but we can apply any complex condition here*/ BEGIN
    insert into ElderCustomers values (@CurrentFirstName,@CurrentAge)
      END


    FETCH NEXT FROM CursorName INTO @CurrentFirstname,@CurrentAge
END

CLOSE CursorName
DEALLOCATE CursorName

如果上面有错误，请提前抱歉

Answer 1

MySQL等价物将是这样的：

BEGIN
  DECLARE CurrentFirstName VARCHAR(300);
  DECLARE CurrentAge INT;
  DECLARE done INT DEFAULT FALSE;
  DECLARE CursorName CURSOR FOR
    SELECT FirstName, Age FROM Customers;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
  OPEN CursorName;
  myloop: LOOP
    FETCH CursorName INTO CurrentFirstName, CurrentAge;
    IF done THEN
      LEAVE myloop;
    END IF;
    IF CurrentAge > 60 THEN
      insert into ElderCustomers values (CurrentFirstName,CurrentAge);
    END IF;
  END LOOP;
  CLOSE CursorName;
END;

最大的区别在于循环，使用CONTINUE HANDLER在没有更多行要提取时设置标志，并在设置标志时退出循环。（这看起来很难看，但这就是在MySQL中完成的方式。）

这个例子引出了一个问题：为什么不写这个（在SQL Server和MySQL中更高效）：

INSERT INTO ElderCustomers (FirstName, Age)
SELECT FirstName, Age
  FROM Customers
 WHERE Age > 60

如何将SQL Server游标转换为MySQL等效

1 个答案: