sql-server-2017

"Capitalize" an entire SQL Server database

It is common practice to keep string capitalized in database. First advantage will be avoiding possible problems which might appear in case of comparing strings.

The next code snippet will generate a script which capitalize all varchar columns in your database. I kindly recommend you to backup database before running this script. I didn’t test it the behavior in case of database contains trigger for update.

SET NO COUNT ON

DECLARE Cur cursor for select name, id from sysobjects where xtype = 'u'
DECLARE @name varchar (255)
DECLARE @id int
DECLARE @Str varchar (8000)

Open Cur
fetch next from Cur into @name, @id

WHILE @@Fetch_Status = 0
BEGIN
    Set @Str = ' Update ' + @name + ' set '
    Update Syscolumns
    set @str = @Str + name + ' = UPPER ( ' + name + ' ) ,'
    where id = @id and xtype in (175, 239, 99, 231, 35, 167)

    set @Str = left (@Str, Len(@Str) - 1)
    PRINT @Str

    fetch next from Cur into @name, @id
END

CLOSE Cur
DEALLOCATE Cur

Empty all tables in SQL Server

In day-by-day programmer life you need a magic script to clean up data you’ve inserted in the application you work on. Of course, you can do this by running ‘CREATE TABLE’ statements and recreate your database from scratch. This is perfect valid, but most of the times you want to keep data in some tables like: configuration tables, catalogues tables, so recreating database is not appropriate in this case.

The following script, interrogates sysobjects table to get all user tables. Then it tries to delete rows from tables. Some of the tables’ rows could be deleted most probably because of reference integrity will be broken. If so, I reiterate all tables and retrying to delete rows. This operation continues until no error is raised while deleting rows from all tables. I must admit this solution uses brute- force, but I found it very simple. I’ve tested it on medium size databases and the results were very good.

If you need to keep data in some tables, you just need to add a clause to the SQL statement getting all user tables in current database:
AND name NOT IN ('author', 'titles', ‘table X’)

SET NOCOUNT ON
DECLARE @TABLE_NAME NVARCHAR(255), @HAS_IDENTITY NUMERIC(15), @HAS_ERROR BIT

-- Create a cursor with all table names
DECLARE TABLES_CURSOR CURSOR SCROLL FOR
SELECT name
FROM sysobjects
WHERE xtype = 'U' AND name <> 'dtproperties'
--AND name NOT IN ('author', 'titles', ...)

SET @HAS_ERROR = 1
OPEN TABLES_CURSOR
WHILE @HAS_ERROR <> 0
BEGIN
       SET @HAS_ERROR = 0
       FETCH FIRST FROM TABLES_CURSOR INTO @TABLE_NAME
       WHILE @@FETCH_STATUS = 0
       BEGIN        
             EXECUTE ('DELETE ' + @TABLE_NAME)
             IF @@ERROR<>0
                    -- Table rows can't be deleted.
                    SET @HAS_ERROR = 1
             ELSE
                    BEGIN
                           --Reset identity for emptied table
                           SET @HAS_IDENTITY = (SELECT IDENT_CURRENT(@TABLE_NAME))
                           IF @HAS_IDENTITY IS NOT NULL
                           BEGIN
                                 DBCC CHECKIDENT (@TABLE_NAME, reseed, 0) WITH NO_INFOMSGS
                           END
                    END

             FETCH NEXT FROM TABLES_CURSOR INTO @TABLE_NAME
       END
END

CLOSE TABLES_CURSOR
DEALLOCATE TABLES_CURSOR

Your suggestions are welcomed.

About fragmentation in SQL Server

- Extent = 8 pages = 64K.
- On a page split, SQL Server generally moves half the total number of rows in the original page to the new page.
- If new rows are added in the order of the clustered index, then the index rows will be always added at the trailing end of the index, preventing the page splits otherwise caused by the INSERT statements.
- For queries that don’t have to traverse a series of pages to retrieve the data, fragmentation can have minimal impact.
- For a table with a clustered index, the fragmentation of the clustered index is the same with the fragmentation of the data pages, since the leaf pages of the clustered index and data pages are the same.
- A small table (or index) with fewer than eight pages is simply unlikely to benefit from efforts to remove the fragmentation because it will be stored on mixed extents.

Internal fragmentation
- When data is fragmented within the same extent (= 8 pages).
- A little internal fragmentation can be beneficial, because it allows you to perform INSERT and UPDATE queries without causing page splits.

External fragmentation
- When data is fragmented over 2 extents.
- A range scan on an index will need more switches between the corresponding extents than ideally required. A range scan on an index will be unable to benefit from read-ahead operations performed on the disk.
- For better performance, it is preferable to use sequential I/O, since this can read a whole extent (8 x 8KB) in a single disk I/O operation. By contrast, a noncontiguous layout of pages requires nonsequential or random I/O operations to retrieve the index pages from the disk, and a random I/O operation can read only 8KB of data in a single disk operation (this may be acceptable, however, if you are retrieving only one.

Columnstore indexes vs indexed views

Columnstore indexes Indexed views
It didn't require Enterprise Edition in SQL Server 2016 SP1+ Limited usage in non-Enterprise Editions
No session setting requirements Requires certain session settings set on
A lot less storage required More storage required
Less administrative overhead / maintenance More administrative overhead / maintenance
Not able to to inserts/updates prior to SQL Server 2014 Most costly to maintain during inserts/updates

Using computed columns in SQL Server

In a database we need some values that were often calculated while generating several reports.

Assuming we have the following table:

CREATE TABLE InvoiceLine
AS
(
       InvoiceLineID int
       , InvoiceID int
       , NumberOfItems int
       , Amount money
)

And we want to find the total amount of an invoice line. We can achieve this by addding a new computed column:

CREATE TABLE InvoiceLine
AS
(
       InvoiceLineID int
       , InvoiceID int
       , NumberOfItems int
       , Amount money
       , TotalAmount AS (Amount*NumberOfItems) PERSISTED
)

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