CASE statement in UPDATE query

UPDATE a
SET a.Date_Added = (CASE 
                    WHEN a.Date_Requested > b.ADmodifyTimeStamp THEN getdate() 
                    ELSE b.ADmodifyTimeStamp END)
FROM [dbo].[tableA] a INNER JOIN [dbo].[tableA] b 
     ON a.[col1] = b.[col1] AND a.[col2] = b.[col2]
WHERE a.[col3] IS NULL

ALTER Table Primary Key

If a primary key already doesn't already exists. then you want to do this

ALTER TABLE provider ADD PRIMARY KEY(person,place,thing);

If a primary key already exists then you want to do this

drop primary key
ALTER TABLE Table1DROP CONSTRAINT PK_Table1_Col1GO


ALTER TABLE [dbo].[tbl_Excel_Tier1Tier2IDs]
   drop constraint [PK_tbl_Excel_Tier1Tier2IDs]
GO


 ALTER TABLE [dbo].[tbl_Excel_Tier1Tier2IDs]
   ADD PRIMARY KEY(Agent_Name, PwC_GUID, Effective_Date);


ALTER TABLE dbo.tblComment_Review
ADD FOREIGN KEY (Record_ID)
REFERENCES [dbo].[tblSurvey_Response_2](Record_ID)

Create List of Calendar Dates

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

SET ANSI_PADDING ON
GO

CREATE TABLE [dbo].[Holidays_Weekends](
CalendarDate datetime NOT NULL,
descr [varchar](20) NULL,
) ON [PRIMARY]

GO

SET ANSI_PADDING OFF
GO


WITH sample AS (
 SELECT CAST('2015-04-01' AS DATETIME) AS dt
 UNION ALL
 SELECT DATEADD(dd, 1, dt)
FROM sample s
  WHERE DATEADD(dd, 1, dt) <= CAST('2015-06-30' AS DATETIME))

INSERT INTO [dbo].[Holidays_Weekends]
SELECT *, '' FROM sample