Question

我希望每天只将数据插入数据库一次。问题是我希望sql查询检查这个（因为代码是不可触摸的）

目前，只要有人访问某个网页，就会调用spInsertRate过程。

INSERT INTO dbo.LU_ExchangeRates 
(exch_Date,exch_Currency,exch_Rate) 
VALUES(@exchDATE,@exchCurrency,@exchRate)

我猜我必须先做一个select语句，如果select语句没有返回一行，那就意味着要运行insert语句。我只是无法弄清楚如何为此编码。

Answer 1

我在exch_Date列上放了一个唯一约束，然后让spInsertRate运行insert并在失败时捕获异常。

Answer 2

如果你必须将它作为单个SQL来实现，那么

INSERT INTO dbo.LU_ExchangeRates 
(exch_Date,exch_Currency,exch_Rate) 
SELECT
   @exchDATE,@exchCurrency,@exchRate
WHERE
   NOT EXISTS ( 
        SELECT * from  dbo.LU_ExchangeRates   
        WHERE   
            exch_Date =  @exchDATE and exch_Currency = @exchCurrency)

但更常见的是

IF  NOT EXISTS ( 
            SELECT * from  dbo.LU_ExchangeRates   
            WHERE   
                exch_Date =  @exchDATE and exch_Currency = @exchCurrency)

    INSERT INTO dbo.LU_ExchangeRates 
    (exch_Date,exch_Currency,exch_Rate) 
    VALUES
       @exchDATE,@exchCurrency,@exchRate

Answer 3

IF NOT EXISTS (SELECT * FROM dbo.LU_ExchangeRates WHERE exch_Date = @exchDATE)
BEGIN
INSERT INTO dbo.LU_ExchangeRates (exch_Date,exch_Currency,exch_Rate)  VALUES(@exchDATE,@exchCurrency,@exchRate) 
END

Answer 4

您可以使用IGNORE_DUP_ROWS选项（或其名称）定义复合唯一索引，然后将以静默方式丢弃任何失败的插入。

这可以在Sybase ASE上完成，也可能不在MS SQL服务器上完成。

Answer 5

如果在表中找不到今天的日期，我会执行单个查询来执行其插入操作。这样，在选择插入之间就没有竞争了。也许

INSERT INTO dbo.LU_ExchangeRates (...)
SELECT @exchDate, ...
 WHERE NOT EXISTS (SELECT *
                     FROM dbo.LU_ExchangeRates
                    WHERE exch_date >= @exchDate
                     AND exch_Currency != @exchCurrency)

每天调用一次插入

5 个答案: