如何在 SQL Server 中组织无限 while 循环?

2022-01-19 00:00:00 loops sql boolean sql-server-2005 sql-server

我想在 SQL Server 2005 中使用无限 WHILE 循环，并在特定条件下使用 BREAK 关键字退出.

I want to use infinite WHILE loop in SQL Server 2005 and use BREAK keyword to exit from it on certain condition.

while true 不起作用，所以我必须使用 while 1=1.有没有更好的方法来组织无限循环?

while true does not work, so I have to use while 1=1. Is there a better way to organize infinite loop ?

我知道我可以使用 goto，但是 while 1=1 begin ... end 在结构上看起来更好.

I know that I can use goto, but while 1=1 begin ... end looks better structurally.

推荐答案

除了 WHILE 1 = 1 正如其他答案所建议的那样，我经常在我的 SQL infintie"中添加超时"" 循环，如下例所示:

In addition to the WHILE 1 = 1 as the other answers suggest, I often add a "timeout" to my SQL "infintie" loops, as in the following example:

DECLARE @startTime datetime2(0) = GETDATE();

-- This will loop until BREAK is called, or until a timeout of 45 seconds.
WHILE (GETDATE() < DATEADD(SECOND, 45, @startTime))
BEGIN
    -- Logic goes here: The loop can be broken with the BREAK command.

    -- Throttle the loop for 2 seconds.    
    WAITFOR DELAY '00:00:02';
END

我发现上述技术在从 long 调用的存储过程中很有用轮询 AJAX 后端.在数据库端使用循环使应用程序不必不断访问数据库以检查新数据.

I found the above technique useful within a stored procedure that gets called from a long polling AJAX backend. Having the loop on the database-side frees the application from having to constantly hit the database to check for fresh data.

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