如果语句 - SQL

Question

我想要实现的是检查表是否存在：

• 如果存在，就截断它
• 如果不存在，则创建表

以下是我的代码，但出现错误。

代码：

--Check if table exists
IF  EXISTS (SELECT * FROM sys.objects 
            WHERE object_id = OBJECT_ID(N'[dbo].[Com_SQL_Server_Agent_Monitor]') 
              AND type in (N'U'))
    TRUNCATE TABLE [dbo].[Com_SQL_Server_Agent_Monitor]
ELSE
    --Create table if not exist
    SET ANSI_NULLS ON
    GO

    SET QUOTED_IDENTIFIER ON
    GO
 
    CREATE TABLE [dbo].[Com_SQL_Server_Agent_Monitor]
    (
        [job_id] [uniqueidentifier] NULL,
        [originating_server] [nvarchar](30) NULL,
        [name] [nvarchar](128) NULL,
        [enabled] [tinyint] NULL,
        [description] [nvarchar](512) NULL,
        [start_step_id] [int] NULL,
        [category] [nvarchar](128) NULL,
        [owner] [nvarchar](128) NULL,
        [notify_level_eventlog] [int] NULL,
        [notify_level_email] [int] NULL,
        [notify_level_netsend] [int] NULL,
        [notify_level_page] [int] NULL,
        [notify_email_operator] [nvarchar](128) NULL,
        [notify_netsend_operator] [nvarchar](128) NULL,
        [notify_page_operator] [nvarchar](128) NULL,
        [delete_level] [int] NULL,
        [date_created] [datetime] NULL,
        [date_modified] [datetime] NULL,
        [version_number] [int] NULL,
        [last_run_date] [int] NULL,
        [last_run_time] [int] NULL,
        [last_run_outcome] [int] NULL,
        [next_run_date] [int] NULL,
        [next_run_time] [int] NULL,
        [next_run_schedule_id] [int] NULL,
        [current_execution_status] [int] NULL,
        [current_execution_step] [nvarchar](128) NULL,
        [current_retry_attempt] [int] NULL,
        [has_step] [int] NULL,
        [has_schedule] [int] NULL,
        [has_target] [int] NULL,
        [type] [int] NULL
    ) ON [PRIMARY]
GO

这是我得到的错误：

数据库中已经有一个名为“Com_SQL_Server_Agent_Monitor”的对象

任何想法我缺少什么？

Answer 1

代码中最大的问题是您的ELSE 块中有多个SQL 语句 - 但它们没有被BEGIN ... END 框住.

所以真的你现在拥有的是：

IF  EXISTS (....)
    TRUNCATE TABLE [dbo].[Com_SQL_Server_Agent_Monitor]
ELSE
    SET ANSI_NULLS ON

-- these statements will be executed ALWAYS - no matter what the
-- IF EXISTS() check returns!    
SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[Com_SQL_Server_Agent_Monitor]
......

所以即使表存在并且被截断 - SET QUOTED_IDENTIFIER ON 和 CREATE TABLE 语句仍将被执行！这就是您收到“表已存在”错误的原因。

你需要做的是：

IF EXISTS (....)
    TRUNCATE TABLE [dbo].[Com_SQL_Server_Agent_Monitor]
ELSE
BEGIN
    SET ANSI_NULLS ON
    SET QUOTED_IDENTIFIER ON

    CREATE TABLE [dbo].[Com_SQL_Server_Agent_Monitor]
    ......
END