Microsoft's SQL Server is a relational database management system (RDBMS) that runs as a server providing multi-user access to a number of databases. It originated from the Sybase SQL Server codebase, which is why both products use the extension of SQL called Transact-SQL (T-SQL).
116
votes
3answers
18k views
What's the difference between a temp table and table variable in SQL Server?
This seems to be an area with quite a few myths and conflicting views.
So what is the difference between a table variable and a local temporary table in SQL Server?
82
votes
14answers
8k views
How do you document your databases?
I find that most of my clients are not documenting their databases at all and I find that pretty scary. To introduce some better practice I would like to know what tools/process you are using.
How ...
63
votes
18answers
8k views
Should developers be able to query production databases?
Should developers be given permission to query (SELECT / read only) production databases? The previous place I worked, the development team had the db_datareader role; where I work now the ...
48
votes
7answers
5k views
Should I index a bit field in SQL Server?
I remember reading at one point that indexing a field with low cardinality (a low number of distinct values) is not really worth doing. I admit I don't know enough about how indexes work to ...
44
votes
4answers
4k views
Why use both TRUNCATE and DROP?
In the system I work on there are a lot of stored procedures and SQL scripts that make use of temporary tables. After using these tables it's good practice to drop them.
Many of my colleagues (almost ...
42
votes
4answers
3k views
Why are numbers tables “invaluable”?
Our resident database expert is telling us that numbers tables are invaluable. I don't quite understand why. Here's a numbers table:
USE Model
GO
CREATE TABLE Numbers
(
Number INT NOT NULL,
...
41
votes
7answers
1k views
Does SQL Server read all of a COALESCE function even if the first argument is not NULL?
I'm using a T-SQL COALESCE function where the first argument will not be null on about 95% of the times it is ran. If the first argument is NULL, the second argument is quite a lengthy process:
...
39
votes
6answers
8k views
How to determine if an Index is required or necessary
I've been running an auto-index tool on our MS SQL database (I modified a script originating from Microsoft that looks at the index statistics tables - Automated Auto Indexing). From the stats, I now ...
32
votes
3answers
5k views
Guid vs INT - Which is better as a primary key?
I've being reading around reasons to use or not Guid and int.
int is smaller, faster, easy to remember, keeps a chronological sequence. And as for Guid, the only advantage I found is that it is ...
30
votes
5answers
6k views
When to use TINYINT over INT?
In general, I always use Ints. I know that in theory this is not the best practice, though, since you should use the smallest data type that will be guaranteed to store the data.
For example, it's ...
29
votes
4answers
2k views
Why does ALTER COLUMN to NOT NULL cause massive log file growth?
I have a table with 64m rows taking 4.3 GB on disk for its data.
Each row is about 30 bytes of integer columns, plus a variable NVARCHAR(255) column for text.
I added a a NULLABLE column with ...
29
votes
9answers
2k views
How can I track database dependencies?
As internal applications evolve over a number of years, you occasionally find there are a number of tables that people believe are no longer relevant and want to cull. What are the practical methods ...
27
votes
3answers
1k views
Is the concept of a clustered index in a DB design sensical when using SSDs?
When designing a SQL server data schema and the subsequent queries, sprocs, views, etc. does the notion of a clustered index and order of data on disk make any sense to consider for DB designs made ...
27
votes
3answers
8k views
Why would SET ARITHABORT ON dramatically speed up a query?
The query is a single select containing a lot of grouping levels and aggragate operations.
With SET ARITHABORT ON is takes less than a second, otherwise it takes several minutes. We have seen this ...
26
votes
4answers
8k views
What are Objective Business Reasons to Prefer SQL Server 2012 over 2008 R2?
My company is facing the decision whether to purchase SQL Server 2012 Denali or SQL Server 2008 R2 for a new database server. I am looking for objective reasons to choose one over the other.
Our ...
26
votes
5answers
2k views
Which database could handle storage of billions/trillions of records?
We are looking at developing a tool to capture and analyze netflow data, of which we gather tremendous amounts of. Each day we capture about ~1.4 billion flow records which would look like this in ...
25
votes
2answers
2k views
Are SQL Server in-place upgrades as ill advised as they used to be?
I have been working with SQL server on and off since SQL Server 6.5, the old advice that still rings in my head was never to do an in-place upgrade.
I'm currently upgrading my 2008 R2 DEV and TEST ...
25
votes
5answers
15k views
What are the main causes of deadlocks and can they be prevented?
Recently one of our ASP.NET applications displayed a database deadlock error and I was requested to check and fix the error. I managed to find the cause of the deadlock was a stored procedure that ...
24
votes
6answers
4k views
What's the difference between a CTE and a Temp Table?
What is the difference between a Common Table Expression (CTE) and a temp table? And when should I use one over the other?
CTE
WITH cte (Column1, Column2, Column3)
AS
(
SELECT Column1, Column2, ...
24
votes
3answers
2k views
On a dedicated database server, how much memory to reserve for the OS?
Assuming you have a dedicated server explicitly for database functions -- how much memory should you reserve for the operating system?
I realize this will probably vary somewhat depending on the ...
23
votes
1answer
1k views
What's the point of WHERE 1=2 for SELECT INTO table query
If we want to create a new table from an existing one in SQL Server we can do the following
SELECT * into Table2
from Table1
WHERE 1=2
Whats the point of where clause? I tried it without the where ...
23
votes
5answers
2k views
Why do sequential GUID keys perform faster than sequential INT keys in my test case?
After asking this question comparing sequential and non-sequential GUIDs, I tried to compare the INSERT performance on 1) a table with a GUID primary key initialized sequentially with ...
23
votes
2answers
769 views
Where can I find database tuning exercises for learning?
As a developer, often DBAs take responsibility for resolving performance issues at the database level so we don't get that much experience diagnosing, tuning, refactoring queries etc.
I'm looking ...
22
votes
3answers
1k views
Performance of Non Clustered Indexes on Heaps vs Clustered Indexes
This 2007 White Paper compares the performance for individual select/insert/delete/update and range select statements on a table organized as a clustered index vs that on a table organized as a heap ...
22
votes
4answers
7k views
When should a primary key be declared non-clustered?
While creating a test database for another question I asked earlier, I remembered about a Primary Key being able to be declared NONCLUSTERED
When would you use a NONCLUSTERED primary key over a ...
22
votes
3answers
9k views
N prefix before string in Transact-SQL query
Would you tell me, please, when should I use N prefix before string in Transact-SQL query? I have started to work with a database where I don't get any results using query like this
SELECT * FROM ...
22
votes
1answer
459 views
In SQL Server, what is the purpose of grouping stored procedures?
One of the most perplexing issues with which I've had to deal has to do with Stored Procedure groups. Given a stored procedure, usp_DoSomethingAwesome, I can create that proc in another group by ...
21
votes
9answers
18k views
Passing array parameters to a stored procedure
I've got a process that grabs a bunch of records (1000's) and operates on them, and when I'm done, I need to mark a large number of them as processed. I can indicate this with a big list of IDs. I'm ...
21
votes
7answers
1k views
What is the difference between a “record” and a “row” in SQL Server?
There was a rather innocuous question about adding dates and times in SQL Server that set off a rather fascinating taxonomic debate.
So how do we differentiate between these related terms and how we ...
21
votes
4answers
1k views
Is NOLOCK always bad?
I am a Report Developer who wants to make my queries as efficient as possible. I used to work with a DBA who told me - I believe because I was always dealing with reports on a Production Server - to ...
20
votes
7answers
2k views
Why should I create an ID column when I can use others as key fields? [duplicate]
Possible Duplicate:
Why use an int as a lookup table's primary key?
So far, I'm accustomed to creating an ID column for every table and it is practical in a way that it makes me not ...
20
votes
1answer
426 views
Reporting Service and Application Role
First poster, long time lurker here.
What is the best way to activate application role in a report ?
I've tried different things and so far the only method that works is to embed the call to the ...
19
votes
7answers
4k views
Writing a simple bank schema: How should I keep my balances in sync with their transaction history?
I am writing the schema for a simple bank database. Here are the basic specifications:
The database will store transactions against a user and currency.
Every user has one balance per currency, so ...
19
votes
3answers
3k views
Is the SQL Server Express memory and CPU limit per instance?
If I have 8GB of RAM in a server and I run 4 instances of SQL Server Express, will the total memory limit used by SQL Server be 1GB or 4GB?
Would it be advisable to run multiple instances like this ...
18
votes
5answers
3k views
Why is there still a varchar data type?
Many of my databases have fields defined as varchars. This hasn't been much of problem since I live and work in America (where the only language that exists is "American". ahem)
After working with ...
18
votes
2answers
3k views
What does a DBA have to know about SSAS?
I've seen a lot of material covering the business aspect of SSAS, but not really much about the important aspects of administration and management.
From the point of view of administering an instance ...
18
votes
4answers
1k views
Why does ORDER BY not belong in a View?
I understand that you cannot have ORDER BY in a view. (At least in SQL Server 2012 I am working with)
I also understand that the "correct" way of sorting a view is by putting an ORDER BY around the ...
17
votes
4answers
2k views
SQL Server “empty table” is slow after deleting all (12 million) records?
I have a SQL Server 2008 instance with approximately 150 columns. I have previously populated this table with approximately 12 million entries, but have since cleared the table in preparation for a ...
17
votes
3answers
2k views
Performance difference for COALESCE versus ISNULL?
I've seen a lot of people use the COALESCE function in place of ISNULL. From internet searches, I've found that COALESCE is ANSI standard, so there is an advantage that we know what to expect when ...
17
votes
5answers
6k views
SQL Server load balancing
What exists today to do Microsoft SQL Server Load Balancing on Windows Server and being transparent to any programatic access. Is this built in or does a solution have to be purchased?
I'm trying to ...
17
votes
2answers
3k views
How to execute SQL against all DBs on a Server
I have some standard SQL that I run against multiple databases on a single server to help me diagnose problems:
select
so.name,
so.type,
MAX(case when sc.text like '%remote%' then '' ...
17
votes
4answers
1k views
What are the consequences of setting varchar(8000)?
Since varchar takes disk space proportional to the size of the field, is there any reason why we shouldn't always define varchar as the maximum, e.g. varchar(8000) on SQL Server?
On create table, if ...
17
votes
5answers
27k views
How to the get current date without the time part
In SQL Server 2005 how do I get the current date without the time part? I have been using GETDATE() but would like it to have a time of 00:00:00.0
16
votes
3answers
11k views
How do I get back some deleted records?
I mistakenly deleted around 2,000,000 records from a remote SQL Server 2008 table. The server is not granting me access to the backup files on the server side.
Is there any way to get back these ...
16
votes
11answers
4k views
Why aren't primary key / foreign key matches used for joins?
As far as I could find out many DBMSs (e.g. mysql, postgres, mssql) use fk and pk combinations only to constrain changes to data, but they are rarely natively used to automatically select columns to ...
16
votes
4answers
7k views
How do I shrink all files quickly for all databases?
In SQL Server (2008 in this case) how can I quickly shrink all the files, both log and data, for all databases on an instance? I could go through SSMS and right click each and choose Tasks -> Shrink, ...
16
votes
3answers
2k views
Justify NOT using (nolock) hint in every query
Have you ever had to justify NOT using a query hint?
I am seeing WITH (NOLOCK) in every single query that hits a very busy server. It is to the point that the developers think it should just be on ...
16
votes
2answers
1k views
Using EXCEPT in a recursive common table expression
Why does the following query return infinite rows? I would have expected the EXCEPT clause to terminate the recursion..
with cte as (
select *
from (
values(1),(2),(3),(4),(5)
) ...
16
votes
3answers
22k views
How to change SQL Server collation
How could I change the SQL Server 2008 R2 Express Default Collation for the whole server and a particular database?
Is there a way to do it using visual interface of SQL Server Management Studio? In ...
16
votes
3answers
4k views
When should I use a unique constraint instead of a unique index?
When I want a column to have distinct values, I can either use a constraint
create table t1(
id int primary key,
code varchar(10) unique NULL
);
go
or I can use a unique index
create table t2(
id ...
