SQL “How To’s” Part 1



When working with SQL, how many times have you come to a situation where you’ve wondered “How do I do this?”.
Although you could find answers by doing some reading from BOL or from some newsgroup, it would be nice to have a kind of a reference material where you can get to-the-point answers. It could save you lot of time and frustration to be able to consult this resource for quick, helpful answers to common questions. This article is an attempt to begin such a reference material.

1) How to display Year as YYYY instead of YY

Enterprise Manager adopts the
User’s regional settings for the date format. By default, the regional setting
for the short date format is m/d/yy. To display it in m/d/yyyy format, follow
the following steps:

On the taskbar, click the Start
button, point to Settings and then select Control Panel. In the Control Panel
dialog box double-click Regional Settings. In the Regional Settings Properties
dialog box, select the Date tab. Next, change the value for the Short Date
Style from M/d/yy to M/d/yyyy.

2) How to Build a Comma Delimited String from Table
values

Sometimes you might want to return your records in a single
comma delimited string. For example, if you have records like :-

Mango

Banana

Peach

Grapes

Strawberry

Instead of returning it as a recordset containing these 5
records, you might want to return them as ‘Mango, Banana, Peach, Grapes,
Strawberry’. Here’s how you can accomplish this.

— Create a temporary table & insert dummy records

Create Table #Fruits (Fruit Varchar(25))
Insert #Fruits (Fruit) values('Mango')
Insert #Fruits (Fruit) values('Banana')
Insert #Fruits (Fruit) values('Peach')
Insert #Fruits (Fruit) values('Grapes')
Insert #Fruits (Fruit) values('Strawberry')

— Build comma delimited string

Declare @Fruits Varchar(200)
Set @Fruits = ''
Update #Fruits
Set @Fruits = @Fruits + Fruit + ','
Set @Fruits = Substring(@Fruits,1,len(@Fruits)-1)
              -- to remove extra comma at the end
print @Fruits

3) How to write values to a Text file

To write a result of a SELECT query in a text file :-

master..xp_cmdshell 'osql -SMyServer -Umyuser -Pmypwd
-Q"select * from products" -dNorthwind  -w"1000" -oc:MyText.txt'

To write a string (like comments, etc.) you can use this
code :-

declare @cmd varchar(1000)
select @cmd = 'echo These are the Products in the
database>> "c:MyText.txt"'
exec master..xp_cmdshell @cmd

4) How to add a User Defined Error Message

Use Master
Go

EXEC sp_addmessage @msgnum = 50001, @severity = 16,
    @msgtext =
N'Failed to insert Customer Transaction into %s table',
    @lang =
'us_english'

Go

You can raise this message from your code like this :-

INSERT Customers (CustomerName)
VALUES ('Rick Nelson')

IF @@Error <> 0
            RAISERROR
(50001,16,1, 'Customers')

5) How to get the Rowcount as well as Error at the same time

Normally when we run a Query, we check if the query was
executed successfully or not before commiting it.

DECLARE @CustomerId            Int
SET @CustomerId = 1

Begin Transaction
Update Orders
Set OrderDate = GetDate()
Where CustomerId = @CustomerId

IF @@Error <> 0
Begin
            Raiserror('Failed
to update Orders',16,1)   
            Rollback
Transaction
End

Commit Transaction

But what if you also want to get the number of records
which were effected by this query? If you do a @@Rowcount after your Error
checking statement then you are going to get 0 as the value of @@Recordcount
would have been reset. And if you place @@Recordcount before the error-checking
statement then your @@Error would get reset. So what’s the solution to get both
of them at the same time ? Save both the values in a local variable and then
check that local variable. Here’s how it can be done.

DECLARE @Rcount                      Int
DECLARE @ErrNum                    Int

DECLARE @CustomerId            Int

SET @Rcount = 0
SET @ErrNum = 0
SET @CustomerId = 1


Begin Transaction
Update Orders
Set OrderDate = GetDate()
Where CustomerId = @CustomerId

SELECT @Rcount = @@RowCount, @ErrNum = @@Error

-- check if there was an error in Updating the records
IF @ErrNum <> 0
Begin
            Raiserror('Failed
to update Orders',16,1)   
            Rollback
Transaction
End

-- check if some records were updated or not
IF @Rcount = 0
Begin
            Raiserror('No
records for CustomerId %d',16,1, @CustomerId)             
            Rollback
Transaction
End

Commit Transaction


Any comments or suggestions are welcome at [email protected].


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Sumit Dhingra

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