Questions tagged [sql-server]

All versions of Microsoft SQL Server (not MySQL). Please also add a version-specific tag, like sql-server-2016, since it is often relevant to the question.

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33
votes
1answer
30k views

SLEEP_TASK Wait Type in SQL Server - What does it indicate?

I haven't seen the SLEEP_TASK wait type before, and today I seem to be getting a ton of them. I'm not the official DBA, just a SQL Server developer who knows some DBA stuff. We upgraded our servers ...
33
votes
1answer
13k views

Why is using a table variable more than twice as fast as a #temp table in this specific case?

I was looking at the article here Temporary Tables vs. Table Variables and Their Effect on SQL Server Performance and on SQL Server 2008 was able to reproduce similar results to those shown there for ...
33
votes
2answers
19k views

Index not making execution faster, and in some cases is slowing down the query. Why is it so?

I was experimenting with indexes to speed up things, but in case of a join, the index is not improving the query execution time and in some cases it is slowing things down. The query to create test ...
32
votes
5answers
198k views

How to handle TimeZone properly in SQL Server?

My local development server is in the Middle East, but my production server is in the UK. I need to show the date to the user in their time zone. For example, if a user is in Saudi Arabia then I ...
32
votes
2answers
8k views

Does the order of columns in a PK index matter?

I have a few very large tables with the same basic strucure. Each one has a RowNumber (bigint) and DataDate (date) column. Data is loaded using SQLBulkImport every night, and no "new" data is ever ...
32
votes
2answers
5k views

As a DBA, how would I go about transitioning from Oracle to SQL Server?

I'm an Oracle DBA that also has Sybase experience. What are the major architectural and conceptual differences between the two RDBMS platforms? An answer similar to the SQL Server->Oracle question ...
32
votes
4answers
5k views

Why does SQL Server return some rows while still executing the query, and sometimes not?

There are queries where when we hit "execute", it shows some rows and it keeps growing, but the query is not over yet. Yet sometimes, it waits until the end of the query. Why does this happen? Is ...
32
votes
2answers
3k views

If a CTE is defined in a query and is never used, does it make a sound?

Do unused CTEs in queries affect performance and / or alter the generated query plan?
32
votes
5answers
28k views

Handling concurrent access to a key table without deadlocks in SQL Server

I have a table that is used by a legacy application as a substitute for IDENTITY fields in various other tables. Each row in the table stores the last used ID LastID for the field named in IDName. ...
32
votes
2answers
58k views

Which one is more efficient: select from linked server or insert into linked server?

Suppose I have to export data from one server to another (through linked servers). Which statement will be more efficient? Executing in source server: INSERT INTO [DestinationLinkedServer].[...
32
votes
1answer
3k views

Very strange performance with an XML index

My question is based on this: https://stackoverflow.com/q/35575990/5089204 To give an answer there I did the following test-scenario. Test scenario First I create a test table and fill it with 100....
32
votes
1answer
64k views

How do I attach a database in SQL Server?

Some common questions relating to attaching databases in SQL Server: What does it mean to attach or detach a database? How do I detach a database? How do I attach a database? What ...
32
votes
2answers
44k views

ISO Week vs SQL Server Week

Okay so I have a report that does a this week vs last week comparison and our customer noticed that their data was "funky". Upon further investigation we found it was not doing weeks correctly ...
32
votes
3answers
37k 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 ...
32
votes
2answers
2k 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 ...
32
votes
5answers
112k views

Logical operators OR AND in condition and order of conditions in WHERE

Let's examine these two statements: IF (CONDITION 1) OR (CONDITION 2) ... IF (CONDITION 3) AND (CONDITION 4) ... If CONDITION 1 is TRUE, will CONDITION 2 be checked? If CONDITION 3 is FALSE, will ...
31
votes
8answers
2k views

Security implications of restoring a backup from an unknown source?

Scenario: You're handed a database backup and told to restore it to a server (that's already hosting other databases), but are given no useful information about what the backup contains or whether the ...
31
votes
1answer
5k views

DBA first day in a new job - check backups and security - How? what else should be checked?

Generally when I start in a new environment, I tend to check where are the backups, when the last full was taken, when was the last restore applied and I check the security too. The way I do this is ...
31
votes
3answers
7k views

Why would a SELECT query cause writes?

I've noticed that on a server running SQL Server 2016 SP1 CU6 sometimes an Extended Events session shows a SELECT query causing writes. For example: The execution plan shows no obvious cause for the ...
31
votes
2answers
6k views

Why does query error with empty result set in SQL Server 2012?

When running the following queries in MS SQL Server 2012 the second query fails but not the first. Also, when run without the where clauses both queries will fail. I am at a loss why either would fail ...
31
votes
6answers
52k views

Load Balancing with SQL Server

What exists today to do Microsoft SQL Server Load Balancing on Windows Server and being transparent to any programmatic access. Is this built in or does a solution have to be purchased? I'm trying to ...
31
votes
1answer
50k views

Cannot execute as the database principal because the principal “dbo” does not exist [duplicate]

I restored a backup of a database from SQL Server 2008 R2 to SQL Server 2012. When I try to access a particular page of my application, I get this error: Cannot execute as the database principal ...
31
votes
3answers
28k views

For absolute performance, is SUM faster or COUNT?

This relates to counting the number of records that match a certain condition, e.g. invoice amount > $100. I tend to prefer COUNT(CASE WHEN invoice_amount > 100 THEN 1 END) However, this is ...
31
votes
5answers
21k views

Make SqlClient default to ARITHABORT ON

First things first: I'm using MS SQL Server 2008 with a database at compatibility level 80, and connecting to it with .Net's System.Data.SqlClient.SqlConnection. For performance reasons I've created ...
31
votes
4answers
29k views

How do I identify the column(s) responsible for “String or binary data would be truncated.”

I am generating some queries automagically with code I wrote to SELECT from a remote Pg database, and insert into a local SQL Server database. However, one of them is generating this error: [...
31
votes
3answers
8k views

What are valid usage scenarios for HEAP tables?

I am currently doing some data imports into a legacy system and discovered that this system does not use a single clustered index. A quick Google search introduced me to the concept of HEAP tables and ...
31
votes
3answers
47k views

What is the difference between Shrink Database and File?

DBCC ShrinkDatabase() DBCC ShrinkFile() Do I need to run both DBCC commands in order to shrink the database? What is the difference between these two above?
31
votes
1answer
1k views

Why is the speed of executing statements dependent on the network connection?

It looks like the speed of executing T-SQL is dependent on the latency of the network connection against the server. I assumed that if SQL Server has nothing to report back to the client about, it ...
31
votes
4answers
8k views

LocalDB v14 creates wrong path for mdf files

Recently, I upgraded LocalDB from version 13 to 14 using the SQL Server Express installer and this instruction. After the installation, I stopped the existing default instance (MSSQLLOCALDB) of ...
31
votes
6answers
182k views

media family on device is incorrectly formed. SQL Server cannot process this media family

I am trying to restore a .BAK in SQL server but get the following error: Msg 3241, Level 16, State 7, Line 1 The media family on device 'c:\glyn\JA.bak' is incorrectly formed. SQL Server cannot ...
31
votes
1answer
14k views

Setting BUFFERCOUNT, BLOCKSIZE, and MAXTRANSFERSIZE for BACKUP command

I am looking for practical guidance for setting the values for the BUFFERCOUNT, BLOCKSIZE, and MAXTRANSFERSIZE of the BACKUP command. I have done a bit of research (see below), I have done a bit of ...
30
votes
7answers
113k views

IntelliSense not working but it is enabled

This problem is really proving to be a tricky one (and quite annoying). In SQL Server Management Studio 2008, up until a few days ago my IntelliSense was working great. Then all of a sudden it ...
30
votes
2answers
8k views

How to make a transition from SQL Server DBA to Oracle?

As an interest, if I would to transition from a SQL Server DBA to Oracle what will be the major learning or unlearning that I would have to do? I would assume the concepts are the same and the ...
30
votes
4answers
14k views

CPU clock speed versus CPU core count - higher GHz, or more cores for SQL Server?

We are beginning to provision a set of physical servers for a virtual cluster of SQL Server 2016 nodes within VMware. We will be utilizing Enterprise Edition licenses. We plan on setting up 6 nodes, ...
30
votes
2answers
43k views

How do I drop all constraints from all tables?

I want to drop all default constraints, check constraints, unique constraints, primary keys and foreign keys from all tables in a SQL Server database. I know how to get all the constraint names from ...
30
votes
5answers
8k views

Why use an int as a lookup table's primary key?

I want to know why I should use an int as a lookup table's primary key instead of just using the lookup value as the primary key (which in most cases would be a string). I understand that using a ...
30
votes
7answers
52k views

What is the most efficient way to get the minimum of multiple columns on SQL Server 2005?

I'm in a situation where I want to get the minimum value from of 6 columns. I've found three ways so far to accomplish this, but I have concerns with the performance of these methods and would like ...
30
votes
6answers
31k views

SQL Server compatibility with New TLS Standards

The major browsers are moving beyond SSL3.0 and TLS1.0 . The PCI Security Council has declared an end-of-life date for these protocols to be considered sufficiently strong encryption. We need to move ...
30
votes
1answer
2k views

Why is a scan faster than seek for this predicate?

I was able to reproduce a query performance issue that I would describe as unexpected. I'm looking for an answer that's focused on internals. On my machine, the following query does a clustered index ...
29
votes
3answers
4k views

Why does SQL Server use a better execution plan when I inline the variable?

I have a SQL query that I am trying to optimize: DECLARE @Id UNIQUEIDENTIFIER = 'cec094e5-b312-4b13-997a-c91a8c662962' SELECT Id, MIN(SomeTimestamp), MAX(SomeInt) FROM dbo.MyTable WHERE Id = @...
29
votes
4answers
891 views

What is a scalable way to simulate HASHBYTES using a SQL CLR scalar function?

As part of our ETL process, we compare rows from staging against the reporting database to figure out if any of the columns have actually changed since the data was last loaded. The comparison is ...
29
votes
5answers
30k views

UPDATE performance where no data changes

If I have an UPDATE statement that does not actually change any data (because the data is already in the updated state). Is there any performance benefit in putting a check in the WHERE clause to ...
29
votes
1answer
3k views

How does SQL Server determine key column order in missing index requests?

How does SQL Server determine the order of key columns in its missing index recommendations for a query plan?
29
votes
5answers
85k views

Restoring a backup to an older version of SQL Server

When trying to restore a backup to a SQL Server Express 2008 database I got the following error: Restore failed for Server '...\SQLEXPRESS'. (Microsoft.SqlServer.SmoExtended) System.Data.SqlClient....
29
votes
6answers
119k views

Copy complete structure of a table

Using some methods, when you create a copy of a table you lose indexes, PK, FK, etc. For example in SQL Server I can say: select * into dbo.table2 from dbo.table1; This is just a simple copy of the ...
29
votes
1answer
2k views

What are Objective Reasons to Prefer SQL Server 2016 over Earlier Versions?

As Microsoft makes SQL Server version upgrades more frequently since the SQL Server 2005 or 2008 days, a lot of companies find it difficult to determine when an upgrade is a "must have!" and when an ...
29
votes
4answers
27k views

Should dbo schema be avoided?

When it comes to the dbo schema: Is it a best practice to avoid using the dbo schema when creating database objects? Why should the dbo schema be avoided or should it? Which database user should own ...
29
votes
4answers
38k views

How can I tell WHY an insert on a certain table is slow?

I know that an INSERT on a SQL table can be slow for any number of reasons: Existence of INSERT TRIGGERs on the table Lots of enforced constraints that have to be checked (usually foreign keys) Page ...
29
votes
2answers
55k views

Is it useful to have the SQL Server instance root directory on a separate drive?

I know it's possible to change many of the default paths when installing SQL Server, and generally when I do an install I change the data and log folders to be on separate drives (typically D and E), ...
29
votes
3answers
9k views

Which PowerShell technique should I use to talk to SQL Server?

I'd ultimately like to use PowerShell to replace the old KornShell scripts we use for SQL instance monitors. I'm having a hard time, though, getting my brain around all the different ways that ...