SQL Server 中 WaitFor 延时执行的用法

在使用这个语句之前，我们先看看微软官方给的帮助文档里面对Waitfor的说明：

2017/03/15

本文内容

语法
参数
备注
示例
另请参阅

Parallel Data Warehouse

Blocks the execution of a batch, stored procedure, or transaction until either a specified time or time interval elapses, or a specified statement modifies or returns at least one row.

Transact-SQL Syntax Conventions

Syntax

syntaxsql

  
WAITFOR   
{  
    DELAY 'time_to_pass'   
  | TIME 'time_to_execute'   
  | [ ( receive_statement ) | ( get_conversation_group_statement ) ]   
    [ , TIMEOUT timeout ]  
}

Arguments

Is the specified period of time that must pass, up to a maximum of 24 hours, before execution of a batch, stored procedure, or transaction proceeds.

time_to_pass is formatted as hh:mm[[:ss].mss].

Is the specified time when the batch, stored procedure, or transaction runs.

time_to_execute is formatted as hh:mm[[:ss].mss] and can optionally include the date of 1900-01-01.

Is a valid RECEIVE statement.

重要

RECEIVE (Transact-SQL).

Is a valid GET CONVERSATION GROUP statement.

重要

GET CONVERSATION GROUP (Transact-SQL).

Specifies the period of time, in milliseconds, to wait for a message to arrive on the queue.

重要

GET CONVERSATION GROUP (Transact-SQL).

Remarks

While executing the WAITFOR statement, the transaction is running and no other requests can run under the same transaction.

If the server is busy, the thread may not be immediately scheduled, so the time delay may be longer than the specified time.

If a query can't return any rows, WAITFOR will wait forever or until TIMEOUT is reached, if specified.

Cursors can't be opened on WAITFOR statements.

Views can't be defined on WAITFOR statements.

sp_who.

monitors the number of WAITFOR statement threads, and randomly selects some of these threads to exit if the server starts to experience thread starvation.

SQL Server identifies these scenarios and returns an empty result set if the chance of such a deadlock exists.

注意

If necessary, adjust the timeout setting for the connection at the application level.

Examples

Using WAITFOR TIME

(22:20).

复制

EXECUTE sp_add_job @job_name = 'TestJob';  
BEGIN  
    WAITFOR TIME '22:20';  
    EXECUTE sp_update_job @job_name = 'TestJob',  
        @new_name = 'UpdatedJob';  
END;  
GO

Using WAITFOR DELAY

The following example executes the stored procedure after a two-hour delay.

复制

BEGIN  
    WAITFOR DELAY '02:00';  
    EXECUTE sp_helpdb;  
END;  
GO

Using WAITFOR DELAY with a local variable

This stored procedure waits for a variable period of time and then returns information to the user as the elapsed numbers of hours, minutes, and seconds.

复制

IF OBJECT_ID('dbo.TimeDelay_hh_mm_ss','P') IS NOT NULL  
    DROP PROCEDURE dbo.TimeDelay_hh_mm_ss;  
GO  
CREATE PROCEDURE dbo.TimeDelay_hh_mm_ss   
    (  
    @DelayLength char(8)= '00:00:00'  
    )  
AS  
DECLARE @ReturnInfo varchar(255)  
IF ISDATE('2000-01-01 ' + @DelayLength + '.000') = 0  
    BEGIN  
        SELECT @ReturnInfo = 'Invalid time ' + @DelayLength   
        + ',hh:mm:ss, submitted.';  
        -- This PRINT statement is for testing, not use in production.  
        PRINT @ReturnInfo   
        RETURN(1)  
    END  
BEGIN  
    WAITFOR DELAY @DelayLength  
    SELECT @ReturnInfo = 'A total time of ' + @DelayLength + ',   
        hh:mm:ss, has elapsed! Your time is up.'  
    -- This PRINT statement is for testing, not use in production.  
    PRINT @ReturnInfo;  
END;  
GO  
/* This statement executes the dbo.TimeDelay_hh_mm_ss procedure. */  
EXEC TimeDelay_hh_mm_ss '00:00:10';  
GO

Here is the result set.

A total time of 00:00:10, in hh:mm:ss, has elapsed. Your time is up.