code 128 check digit c# Querying the dbo.Test table in Visual C#

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Listing 2 Querying the dbo.Test table
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--view the table SELECT * FROM dbo.Test ;
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To examine the amount of space the table consumes, we ll use a Dynamic Management View (DMV) called sys.dm_db_index_physical_stats. DMVs were first introduced in SQL Server 2005 and have been continued in SQL Server 2008. (For more on DMVs, see chapter 29, My favorite DMVs, and why, by Aaron Bertrand.)
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The scripts that make use of DMVs will not work in SQL Server 2000.
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The query in listing 3 returns a single row of data with four columns the allocation unit type, the page count, the average page space used as a percentage, and the total
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Results from dbo.Test table
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Understanding how SQL Server automatically reuses table space
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number of rows in the dbo.Test table. The alloc_unit_type_desc column describes the allocation unit type: valid values are IN_ROW_DATA, LOB_DATA, or ROW_OVERFLOW_DATA (see Books Online for a detailed explanation of these terms). The page_count column indicates the total number of data pages used by the table for IN_ROW_DATA (that is, the allocation unit that stores the table rows in our example). The avg_page_ space_used_in_percent column reports the average percentage of space used in all data pages in the IN_ROW_DATA allocation type. The record_count intuitively contains the number of rows contained in the table.
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Listing 3 Examining the space used by the dbo.Test table
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--check the size of the table SELECT alloc_unit_type_desc ,page_count ,avg_page_space_used_in_percent ,record_count FROM sys.dm_db_index_physical_stats( DB_ID() ,OBJECT_ID(N'dbo.Test') ,NULL ,NULL ,'Detailed') ;
Figure 2 displays the results of the DMV query. As you can see on my test system, 158 data pages are used to store the 1,000 rows and each data page is, on average, 82.1 percent full.
Figure 2 Using a DMV to review space used
To continue with the example, let s delete half of the rows in our dbo.Test table and see what happens to the space used by the table. The T-SQL script in listing 4 uses the modulo operator, represented by the percent sign in T-SQL, to delete each row where the value in the first column, col1, is an odd number. So we are deleting every other row in the table.
Listing 4 Deleting the odd-numbered rows
--delete the odd rows DELETE FROM Test WHERE col1 % 2 = 1 --view the table SELECT *
FROM dbo.Test ;
Reusing space in a table
Figure 3 shows the results of the SELECT query. You can see that the table is left with test row #2, test row #4, and so on, for a total of 500 rows.
Figure 3 Deleting half the rows in the dbo.Test table
Now that half of the rows in the table have been deleted, let s look at the space the table consumes by running the DMV query from listing 3 again. Figure 4 shows that the number of pages used to store the table s data remains constant but the percentage used of each page changes. It is cut in half, from 82.1 percent to 42.1 percent. Also notice that the number of rows reported in the record_count column has been cut in half, as expected.
Figure 4 Examining the space consumed by the dbo.Test table
So let s add some new rows to the table to prove that SQL Server will automatically reuse the newly freed space, thus filling in the holes, to go back to our Access comparison. Using the T-SQL script found in listing 5, we can quickly add 500 rows of data to the dbo.Test table. This script is similar to the one first used to populate the table with sample data. It inserts one row at a time in a WHILE loop. To help differentiate the new rows from the existing rows, I change the insert statement so that the third column is filled with WXYZ s rather than ABCD s as before, though it doesn t matter for our proof.
Listing 5 Adding new rows to the dbo.Test table
--add some more test data DECLARE @cnt INT ; SET @cnt = 0 ; WHILE @cnt < 500 BEGIN SELECT @cnt = @cnt + 1 ; INSERT dbo.Test ( col1,col2,col3 ) VALUES ( @cnt ,'test row # ' + CAST(@cnt AS VARCHAR(10))
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