Question

我需要帮助才能理解为什么下面的循环不起作用。它只会插入第一个记录然后停止。

DECLARE 
@NEW_BALANCE            FLOAT
, @CUR_NEW_BALANCE      FLOAT
, @OLD_BALANCE          FLOAT
, @CUR_OLD_BALANCE      FLOAT
, @INITIAL_BALANCE      FLOAT
, @RATE                 FLOAT
, @MONTHLY_RATE         FLOAT
, @MONTHLY_INTEREST     FLOAT
, @PAYMENT              FLOAT



SELECT @RATE    = INTEREST
    FROM ACCOUNTS WHERE ACCOUNT = 'AMEXDELTA'

SET @MONTHLY_RATE               = (@RATE / 12) / 100

SELECT TOP 1 @CUR_NEW_BALANCE       = NEW_BALANCE
             , @CUR_OLD_BALANCE     = OLD_BALANCE
FROM PAYMENTS ORDER BY ID DESC

SELECT @CUR_NEW_BALANCE AS NEW_BALANCE
       , @CUR_OLD_BALANCE AS OLD_BALANCE

WHILE @NEW_BALANCE > 0
BEGIN

    SET @MONTHLY_INTEREST               = (@CUR_OLD_BALANCE * @MONTHLY_RATE)

    SET @OLD_BALANCE                    = (@CUR_NEW_BALANCE - @PAYMENT)

    SET @NEW_BALANCE                    = (@MONTHLY_INTEREST + @OLD_BALANCE)


    INSERT INTO PAYMENTS(PAYMENT, MONTHLY_INTEREST, OLD_BALANCE, NEW_BALANCE)
        SELECT @PAYMENT, @MONTHLY_INTEREST, @OLD_BALANCE, @NEW_BALANCE


END

以下是PAYMENTS表中的当前数据：

Old_Balance | New_Balance
------------|------------
2845.8      | 2845.8

以下是表ACCOUNTS

中的当前日期

Interest
--------
15.24

Answer 1

@NEW_BALANCE尚未初始化。它是NULL，不大于0（未定义）。

DECLARE 
@NEW_BALANCE            FLOAT

Select @NEW_BALANCE

输出：

----------------------
NULL

(1 row(s) affected)

所以，初始化它：

DECLARE 
@NEW_BALANCE            FLOAT = 0

Select @NEW_BALANCE

虽然SQL中的循环不起作用

1 个答案: