Solved

NULL values in sql-server

Posted on 2000-03-20
10
209 Views
Last Modified: 2008-03-17
Do recordfields containing NULL-values take up storage space? (SQL-server 7)
0
Comment
Question by:pietjepuk
10 Comments
 
LVL 142

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 2636233
Yes, but only a few bytes (indicating that there is a NULL value)
0
 
LVL 1

Author Comment

by:pietjepuk
ID: 2636274
In this specific situation a few bytes might very well add up to Gigabytes. Do you (or anyone) know exactly how many bytes?
0
 
LVL 2

Expert Comment

by:evertd
ID: 2636536
I think that is not documented but you can try to load 1000000 rows with NULL values and a table without the null values. Than look the size differences of the two tables.
0
 
LVL 142

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 2636618
M$ reference:
For each variable-sized column (including nullable columns), byte usage is:
1 (or more) shared bytes per table  indicating columns are null or not (2 if more than 8 columns
0 byte per column that is null
0
 
LVL 3

Expert Comment

by:ahoor
ID: 2641065
Also depends on the datatype.
0
NAS Cloud Backup Strategies

This article explains backup scenarios when using network storage. We review the so-called “3-2-1 strategy” and summarize the methods you can use to send NAS data to the cloud

 
LVL 142

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 2643408
ahoor: if value is null, datatype is not important: size is 0 bytes, the nullbit mask will be defined whatsoever and take 1 or more bytes (depending on the number of nullable columns in the table)
0
 
LVL 1

Author Comment

by:pietjepuk
ID: 2643655
Adjusted points from 50 to 100
0
 
LVL 1

Author Comment

by:pietjepuk
ID: 2643656
evertd, thanks for the suggestion but it doesn't answer my question(s).

angelIII,
So this nullbit mask uses bits (eight columns make up one byte). But does it refer to the nullability of columns, or to actual storage of null values?
0
 
LVL 142

Accepted Solution

by:
Guy Hengel [angelIII / a3] earned 100 total points
ID: 2644167
The nullability of columns is referred to in the syscolumns table, with the exact definition of every column (type, size...)
Then for every row, the values are stored one after the other (fixed sized columns first), with some bytes of informations (number of columns, size of row...) This bytes include the nullbit-mask (taking 0 to n bytes).
So the answer is, this nullbit mask refers to the actual value of NULLS
0
 
LVL 1

Author Comment

by:pietjepuk
ID: 2644388
OK, (I think) I get it. Through this nullbit masking up to 8 columns that are NULL can be stored into 1 byte (per row), right?

Thanks again.

Pietjepuk.
0

Featured Post

Optimizing Cloud Backup for Low Bandwidth

With cloud storage prices going down a growing number of SMBs start to use it for backup storage. Unfortunately, business data volume rarely fits the average Internet speed. This article provides an overview of main Internet speed challenges and reveals backup best practices.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Having an SQL database can be a big investment for a small company. Hardware, setup and of course, the price of software all add up to a big bill that some companies may not be able to absorb.  Luckily, there is a free version SQL Express, but does …
Slowly Changing Dimension Transformation component in data task flow is very useful for us to manage and control how data changes in SSIS.
This video shows, step by step, how to configure Oracle Heterogeneous Services via the Generic Gateway Agent in order to make a connection from an Oracle session and access a remote SQL Server database table.
Via a live example, show how to extract insert data into a SQL Server database table using the Import/Export option and Bulk Insert.

919 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

20 Experts available now in Live!

Get 1:1 Help Now