How to rename a column in a SQL Server table without using the designer

If you have a table and you want to rename a column without using the designer, how can you do that?

First create this table

CREATE TABLE TestColumnChange(id int)
INSERT TestColumnChange VALUES(1)


SELECT * FROM TestColumnChange

As you can see the select statement returns id as the column name. you can use ALTER table ALTER Column to change the dataype of a column but not the name.

Here is what we will do, execute the statement below

EXEC sp_rename 'TestColumnChange.[id]', 'value', 'COLUMN'


Now do the select, you will see that the column name has changed

SELECT * FROM TestColumnChange

That is it, very simple

Do You Know How Between Works With Dates?

Do you use between to return data that has dates? Do you know that between will get everything since midnight from the first criteria and up to midnight exactly from the second criteria. If you do BETWEEN 2006-10-01 AND 2006-10-02 then all the values that are greater or equal than 2006-10-01 and less or equal to 2006-10-02 will be returned. So no values after 2006-10-02 midnight will be returned.

Let's test this out, first let's create this table

CREATE TABLE SomeDates (DateColumn DATETIME)

Insert 2 values
INSERT INTO SomeDates VALUES('2006-10-02 00:00:00.000')
INSERT INTO SomeDates VALUES('2006-10-01 00:00:00.000')

Return everything between '2006-10-01' and '2006-10-02'
SELECT *
FROM SomeDates
WHERE DateColumn BETWEEN '20061001' AND '20061002'
ORDER BY DateColumn
This works without a problem

Let's add some more dates including the time portion
INSERT INTO SomeDates VALUES('2006-10-02 00:01:00.000')
INSERT INTO SomeDates VALUES('2006-10-02 00:00:59.000')
INSERT INTO SomeDates VALUES('2006-10-02 00:00:01.000')
INSERT INTO SomeDates VALUES('2006-10-01 00:01:00.000')
INSERT INTO SomeDates VALUES('2006-10-01 00:12:00.000')
INSERT INTO SomeDates VALUES('2006-10-01 23:00:00.000')


Return everything between '2006-10-01' and '2006-10-02'
SELECT *
FROM SomeDates
WHERE DateColumn BETWEEN '20061001' AND '20061002'
ORDER BY DateColumn
Here is where it goes wrong; for 2006-10-02 only the midnight value is returned the other ones are ignored


Now if we change 2006-10-02 to 2006-10-03 we get what we want
SELECT *
FROM SomeDates
WHERE DateColumn BETWEEN '20061001' AND '20061003'
ORDER BY DateColumn

Now insert a value for 2006-10-03 (midnight)

INSERT INTO SomeDates VALUES('2006-10-03 00:00:00.000')

Run the query again
SELECT *
FROM SomeDates
WHERE DateColumn BETWEEN '20061001' AND '20061003'
ORDER BY DateColumn

We get back 2006-10-03 00:00:00.000; between will return the date if it is exactly midnight

If you use >= and < then you get exactly what you need
SELECT *
FROM SomeDates
WHERE DateColumn >= '20061001' AND DateColumn < '20061003'
ORDER BY DateColumn

--Clean up
DROP TABLE SomeDates


So be careful when using between because you might get back rows that you did not expect to get back and it might mess up your reporting if you do counts or sums

Five Ways To Return Values From Stored Procedures

I have answered a bunch of questions over the last couple of days and some of them had to do with returning values from stored procedures
Everyone knows that you can return a value by using return inside a stored procedure. What everyone doesn't know is that return can only be an int data type
So how do you return something that is not an int (bigint, smallint etc etc) datatype
Let's take a look
We will start with a regular return statement, everything works as expected

--#1 return
CREATE PROCEDURE TestReturn
AS
SET NOCOUNT ON

DECLARE @i int
SELECT @i = DATEPART(hh,GETDATE())
RETURN @i
SET NOCOUNT OFF
GO

DECLARE @SomeValue int
EXEC @SomeValue = TestReturn
SELECT @SomeValue
GO


Now let's try returning a varchar

ALTER PROCEDURE TestReturn
AS
SET NOCOUNT ON

DECLARE @i VARCHAR(50)
SELECT @i = DATENAME(mm,GETDATE())
RETURN @i
SET NOCOUNT OFF
GO

DECLARE @SomeValue VARCHAR(50)
EXEC @SomeValue = TestReturn
SELECT @SomeValue
GO

Oops, it doesn't work the following message is returned (if you run it in September)
Server: Msg 245, Level 16, State 1, Procedure TestReturn, Line 7
Syntax error converting the varchar value 'September' to a column of data type int.

Let's try hard coding a character value
ALTER PROCEDURE TestReturn
AS
SET NOCOUNT ON
RETURN 'ab'
SET NOCOUNT OFF
GO


DECLARE @SomeValue VARCHAR(50)
EXEC @SomeValue = TestReturn
SELECT @SomeValue
GO

It is interesting that the procedure compiles without a problem. But when we try to run it the following message is displayed


Server: Msg 245, Level 16, State 1, Procedure TestReturn, Line 7
Syntax error converting the varchar value 'ab' to a column of data type int.


So what can we do? well we can use an OUTPUT parameter. By the way the following 4 ways to return a varchar values are in the order from best to worst

--#2 OUTPUT
ALTER PROCEDURE TestReturn @SomeParm VARCHAR(50) OUTPUT
AS
SET NOCOUNT ON
SELECT @SomeParm = 'ab'
SET NOCOUNT OFF
GO


DECLARE @SomeValue VARCHAR(50)
EXEC TestReturn @SomeParm = @SomeValue OUTPUT
SELECT @SomeValue
GO


Another way is to create a temp table and call the proc with insert..exec

--#3 Insert Into TEMP Table outside the proc
ALTER PROCEDURE TestReturn
AS
SET NOCOUNT ON
SELECT 'ab'
SET NOCOUNT OFF
GO

DECLARE @SomeValue VARCHAR(50)
CREATE TABLE #Test(SomeValue VARCHAR(50))
INSERT INTO #Test
EXEC TestReturn
SELECT @SomeValue = SomeValue
FROM #Test

SELECT @SomeValue
DROP TABLE #Test
GO


This one is almost the same as the previous example, the only difference is that ther insert happens inside the proc
And of course if you call the proc without creating the table you will get a nice error message

--#4 Insert Into TEMP Table inside the proc
ALTER PROCEDURE TestReturn
AS
SET NOCOUNT ON
INSERT INTO #Test
SELECT 'ab'
SET NOCOUNT OFF
GO


DECLARE @SomeValue VARCHAR(50)
CREATE TABLE #Test(SomeValue VARCHAR(50))
EXEC TestReturn
SELECT @SomeValue = SomeValue
FROM #Test

SELECT @SomeValue
DROP TABLE #Test


And last you create a permanent table with an identity, in the proc you insert into that table and you return the identity value. You can then use that identity value to get the varchar value

--#5 Insert Into A Table And Return The Identity value
CREATE TABLE HoldingTable(ID INT IDENTITY,SomeValue VARCHAR(50))
GO

ALTER PROCEDURE TestReturn
AS
SET NOCOUNT ON
DECLARE @i INT

INSERT INTO HoldingTable
SELECT 'ab'
SELECT @I = SCOPE_IDENTITY()

RETURN @i
SET NOCOUNT OFF
GO

DECLARE @SomeValue VARCHAR(50), @i INT
EXEC @i = TestReturn
SELECT @SomeValue = SomeValue
FROM HoldingTable
WHERE ID = @i

SELECT @SomeValue



DROP PROCEDURE TestReturn

Fun With SQL Server Update Triggers

Below is some code that will show how to test for updated field values in an update trigger. As you can see the IF UPDATE (field) is true even when the values don’t change. Another thing to keep in mind is that if a value changes from NULL to something else and vice-versa, and you are comparing deleted and inserted tables without using COALESCE or ISNULL it won’t return those rows. Run the code below to see what I mean


CREATE TABLE TestTrigger (TestID INT identity,
name VARCHAR(20),
value DECIMAL(12,2) ,
CONSTRAINT chkPositiveValue CHECK (value > 0.00) )


INSERT INTO TestTrigger
SELECT 'SQL',500.23


CREATE TRIGGER trTest
ON TestTrigger
FOR UPDATE
AS

IF @@ROWCOUNT =0
RETURN

IF UPDATE(value)
BEGIN
SELECT '1', * FROM deleted d JOIN inserted i ON d.testid =i.testid
SELECT '2',* FROM deleted d JOIN inserted i ON d.testid =i.testid
AND i.value <> d.value
SELECT '3',* FROM deleted d JOIN inserted i ON d.testid =i.testid
AND COALESCE(i.value,-1) <> COALESCE(d.value,-1)
END
GO

--Let's update the value to 100
UPDATE TestTrigger SET value = 100 WHERE testid =1
--we get back all 3 rows


--Let's run the same statement
UPDATE TestTrigger SET value = 100 WHERE testid =1
--we get back the first row


--Let's really update
UPDATE TestTrigger SET value = 200 WHERE testid =1
--we get back all 3 rows

--Let's update with NULL
UPDATE TestTrigger SET value =NULL WHERE testid =1
--we get back rows 1 and 3, row 2 is not returned because it can't compare it

--Let's update with NULL again
UPDATE TestTrigger SET value =NULL WHERE testid =1
--we get back row 1

--Let's update with 300
UPDATE TestTrigger SET value =300 WHERE testid =1
--we get back rows 1 and 3, row 2 doesn't return because it can't compare NULL to 300

--Let's update with 500
UPDATE TestTrigger SET value =500 WHERE testid =1
--we get back all 3 rows