更新SQL Server 2005中的表格列

Question

I check for the existence of a column in a table. If it exists, I update a column in a 2nd table based on the column in first table.

The issue is, the update is getting executed when it should not be and results in an error.

I check for the existence of column Requested_by in table Service_requests_details , I then update a column in service_requests based on column requested_by in table Service_Requests_Details .

The point is, Requested_By might not exist in table Service_requests_details .

IF EXISTS (SELECT * FROM sys.columns WHERE Name = N'Requested_By' and object_ID = object_ID(N'Service_Requests_Details'))
BEGIN
      Update SR
      Set SR.Requested_By  = SRD.Requested_By 
      FROM Service_Requests SR
      INNER JOIN Service_Requests_Details SRD ON SRD.Request_Index = SR.Service_Request_Index
END
GO

Update:
Thanks everyone who responded. Thanks @SqlAcid for the answer.

Answer 1

The problem is the parser will still evaluate your update statement and fail even when the IF EXISTS is false; you could use sp_executesql to get around it:

declare @sql nvarchar(1000)
IF EXISTS (SELECT * FROM sys.columns WHERE Name = N'Requested_By' and object_ID = object_ID(N'Service_Requests_Details')) 
BEGIN 
  set @sql = 'Update SR 
      Set SR.Requested_By  = SRD.Requested_By  
      FROM Service_Requests SR 
      INNER JOIN Service_Requests_Details SRD ON SRD.Request_Index = SR.Service_Request_Index'
  exec sp_executesql @sql
END 
GO 

Answer 2

This is what I would do in SQL 2008, don't have a SQL 2005 instance handy to see if it works in there, but worth a try:

IF EXISTS (SELECT * FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'Service_Requests_Details' AND COLUMN_NAME = 'Requested_By')
BEGIN
    ...
END