SQL Server

Some TSQL Anti-patterns: ‘DISTINCT’ column list, Scalar valued Functions…

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I’ve been looking through some code that I last worked on over a year ago. Since then several people have contributed to the project. The first thing that I noticed was a sprinkling of DISTINCT added to SELECT queries where it was originally totally unnecessary! Paul White puts it better than I could:

“SELECT DISTINCT is sometimes an indication that someone has ‘fixed’ a query that returns duplicate rows in a naive way. This (mis-)use is probably more common among those with relatively little database experience.” https://dba.stackexchange.com/questions/139687/when-to-use-distinct

If you’re a Dev or DBA and you’re about to fix a problem by adding DISTINCT to a query, ask yourself “I am really fixing the real problem?”. And if DISTINCT is the real answer, then an equivalent GROUP BY might be more efficient.

The next thing I noticed is the addition of scalar valued functions not unsurprisingly causing less than stellar performance. An experienced DBA (and developer) should be fully aware of the performance implications of using scalar valued functions, and should avoid if possible.

 

SQL Server 2012 Error: No catalog entry found for partition ID xxx in database N

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If you are running SQL Server 2012 and you see this error:

DESCRIPTION: No catalog entry found for partition ID xxx in database N.
The metadata is inconsistent. Run DBCC CHECKDB to check for a metadata 
corruption.

a quick check reveals database 2 is tempDB:

SELECT name FROM sys.databases WHERE database_id = 2;

If you run a DBCC CHECKDB against tempDB:

DBCC CHECKDB ('tempdb') WITH NO_INFOMSGS, TABLERESULTS;

you receive no results, indicating no issues with tempDB.

This is a known issue with a fix:

FIX: “No catalog entry found for partition ID in database ” error when you use SQL Server 2012

Assume that you query the tempdb.sys.allocation_units table in Microsoft SQL Server 2012. When you use NOLOCK hint in the query or the query is under the READ UNCOMMITED transaction isolation level, you receive the following intermittent 608 error message:

Error: 608 Severity: 16 State: 1
No catalog entry found for partition in database . The metadata is inconsistent. Run DBCC CHECKDB to check for a metadata corruption

Note The DBCC CHECKDB command does not show any sign of database corruption.

Fixed in:

 

SSMS: Tips and Tricks to Enhance Productivity

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Set colours to differentiate between servers/environments

You can set SSMS connection properties to give a visual indication of which server your queries are connected to.

When you connect to a SQL Server instance, click on the ‘Options’ button:

ssms1

Then click on the ‘Connection Properties’ tab and choose a custom colour for your connection:

ssms2

Suggested colours for your environments:

  • Production – Red
  • UAT – Orange
  • QA – Yellow
  • Dev – Blue
  • Local – Green

Once set, every time you open a connection to a server, it will display the assigned colour in the SSMS status bar.

Configure SSMS tabs to only show file names

Follow Brent Ozar’s simple instructions here: SSMS 2016: It Just Runs More Awesomely (It’s not just for SSMS 2016). This makes tabs easier to read and pinning tabs is a great idea for often used scripts. [I also like to set my status bar position to the top of the query window]:

ssms3

While you are in the Options dialog, go to Tools -> Options -> Environment -> AutoRecover and make sure AutoRecover files is turned on, with appropriate values set.

Cycle through clipboard text

All Windows users will be familiar with the shortcut keys CTRL+C and CTRL+V. The ‘Cycle Clipboard Ring’ feature in SSMS keeps track of last 20 items you have cut/copied. You can use CTRL+SHIFT+V to paste the last copied item from the clipboard just as you would with CTRL+V. If you repeatedly press CTRL+SHIFT+V, you cycle through the entries in the Clipboard Ring, selecting the item you want to paste.

This also works in Visual Studio 2015+

List all columns in a table

To quickly list all the columns in a table as a comma separated list, simply drag the ‘Columns’ folder in Object Explorer and drop it onto a query window. This creates a single line of comma separated column names; if you want to format as one column per line, you can use a search and replace utilising a newline with the regex search option turned on.

Highlight the comma separated list of columns you just created, type CTRL+H, turn on regular expression searching, enter a comma followed by a space ,  as the search text, and replace with a comma followed by a newline ,\n

ssms4

Disable Copy of Empty Text

Ever had this happen to you? You select a block of text to copy, move to the place you want to paste it, and then accidentally hit CTRL+C again instead of CTRL+V. Your block of copied text has been replaced by an empty block!

You can disable this behaviour (I have no idea why disabled is not the default): go to Tools -> Options -> Text Editor -> All Languages -> General -> ‘Apply Cut or Copy Commands to blank lines when there is no selection’ and uncheck the checkbox.

ssms7

Set Tabs to Insert 4 Spaces

Avoid indentation inconsistencies when opening TSQL files in different editors: go to Tools -> Options -> Text Editor -> Transact-SQL -> Tabs -> Insert Spaces and click the radio button. Set Tab and indent size to 4.

Use GO X to Execute a Batch or Statement Multiple Times

The ‘GO’ command is not a Transact SQL statement but marks the end of a batch of statements to be sent to SQL Server for processing. By specifying a number after ‘GO’ the batch will be run the specified number of times. You can use this to repeat  statements for creating test data. This can be a simpler alternative to writing a cursor or while loop.

create table MyTestTable
(
Id int not null identity(1,1) primary key,
CreatedDate datetime2
)
GO

This will run the insert statement 100 times:

insert into MyTestTable(CreatedDate)select GetDate()
GO 100

Templates and Code Snippets

Many users are not aware of SSMS’s Template Browser. These templates contain placeholders/parameters that help you to create database objects such as tables, indexes, views, functions, stored procedures etc.

By default when you open SSMS, the Template Explorer isn’t visible.  Press Ctrl+Alt+T or use the View -> Template Explorer menu to open it. One of my favourite templates is the database mail configuration:

ssms8

Template Explorer provides a view of a folder structure inside the SSMS installation, which is located at C:\Program Files (x86)\Microsoft SQL Server\XXX\Tools\Binn\ManagementStudio\SqlWorkbenchProjectItems\Sql

Templates contain parameter place holders: press Ctrl + Shift + M to open a dialog box that substitutes values for the template place holders:

ssms9

You can also add your own templates. Right-click on the SQL Server Templates node of the Explorer and choose New -> Folder and set the folder name. Then right-click on the folder and choose New -> Template. Add your code, with any parameters defined as:

< ParameterName, Datatype, DefaultValue >

Click Ctrl + Shift + M to check the parameter code blocks are well formed.

Code snippets are similar but simpler without parameters. Type CTRL + K + X to insert a code snippet.

Registered Servers

Most users have a number of servers they frequently connect to. The Registered Servers feature allows you to save the connection information of these frequently accessed servers.

You can create your own server groups, perhaps grouped by environment or by project.

Navigate to View -> Registered Servers. Then right-click on the ‘Local Server Groups’ and click on ‘New Server Registration’, and enter your connection details.

There is also a feature that allows windows only authentication to be used against a central server management server

Built in Performance Reports in SSMS

SSMS provides a number of built in standard reports. To access the database level reports, right click on a Database –> Reports –> Standard Reports –> Select a Report:

ssms6

 Useful SSMS Keyboard Shortcuts

Shortcut Action
CTRL+N Open new query with current database connection
CTRL+O Open a file in a new tab with current database connection
CTRL+R Toggle between displaying and hiding Results Pane
CTRL+M Include actual query execution plan
CTRL+L Display estimated query execution plan
CTRL+TAB Cycle through query windows
F4 Display the Properties Window
CTRL + ] Navigate to the matching parenthesis
CTRL+ALT+T Open Template Explorer
CTRL+SHIFT+M Specify values for Template parameters
CTRL+K+X Insert SQL code snippets
CTRL+SHIFT+U Change text to upper case
CTRL+SHIFT+L Change text to lower case
CTRL+K+C / CTRL+K+U Comment / Uncomment selected text
CTRL+F / CTRL+H Find / Replace

Splitting the Query Window to work on large queries

The query window can be split into two panes so that you can view two parts of the same query simultaneously. To split the window, simply drag the splitter bar at the top right hand side of the query window downwards. Both parts of the split window can be scrolled independently. This is useful if you have a large query and want to compare different parts of the same query.

ssms5

Vertical Block Select Mode

This is a feature I use often. You can use it to select multiple lines or a block of text over multiple lines, you can type text and it will be entered across all the selected rows, or you can paste blocks of text. To use it, hold down the ALT key, then left click on your mouse to drag the cursor over the text you want to select and type/paste the text you want to insert into multiple lines.

Keyboard Shortcut – ALT + SHIFT + Arrow Keys
Mouse – ALT + Left-Click + Drag

Object Explorer details

The Object Explorer Details window is a feature which very few developers use (including me, as I always forget it’s there!). It lists all the objects in a server and additional information like Row Count, Data Space Used, Index Space Used etc. It’s a quick way to see table row counts for all tables in a database.

The Object Explorer Details window is not visible by default. Click F7 or navigate to View -> Object Explorer Details to open it. To add columns, right click on the column header row and select those columns you want to see.

ssms10

Display Query Results in a Separate Tab

If you want to focus on the results after you run a query, and would like to give it as much screen real estate as possible, go to Tools -> Options -> Query Results -> SQL Server -> Results To Grid and enable the option “Display Results in a separate tab”.

Do you Encrypt your Remote Connections to SQL Azure Databases?

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If you’re not encrypting connections to SQL Azure (or any remote SQL Server instance), then you probably should.

Encrypted connections to SQL Server use SSL,  and that is about as secure as you can get (currently).

[Remember: SSL protects only the connection, i.e. the data as it is transmitted ‘on the wire’ between the client and SQL Server. It says nothing about how the data is actually stored on the server].

Update: Don’t forget to also set TrustServerCertificate=false

SSMS

When you open SSMS’s ‘Connect to Server’ dialog, click the bottom right ‘Options’ button, and make sure you tick the checkbox ‘Encrypt Connection’:

image

SQLCMD

Ensure you add the -N command line option. The -N switch is used by the client to request an encrypted connection. This option is equivalent to the ADO.net option ENCRYPT = true.

e.g.

sqlcmd –N –U username –P password  –S servername –d databasename –Q “SELECT * FROM myTable”

Linked Servers

When creating a linked server to SQL Azure,  the @provstr parameter must be set to ‘Encrypt=yes;’:

-- Create the linked server:
EXEC sp_addlinkedserver
@server     = 'LocalLinkedServername',
@srvproduct = N'Any',
@provider   = 'SQLNCLI',
@datasrc    = '???.database.windows.net', -- Azure server name
@location   = '', 
@provstr    = N'Encrypt=yes;',       -- <<--  Important!
@catalog    = 'RemoteDatabaseName';  -- remote(Azure) database name
go

 

ADO.NET Connection strings

Add “ENCRYPT = true” to your connection string, or set the SqlConnectionStringBuilder property to True.

[Remember: don’t distribute passwords by sending as plaintext over the Internet, i.e. don’t email passwords! ]

SQL Server and SQL Azure: Clear Plan Cache

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For on-premise SQL Servers you can run

dbcc freeproccache

which clears the entire server cache (provided you have the ALTER SERVER STATE permission). Many online resources and SQL Server Books Online give scary warnings about running this, but running DBCC FREEPROCCACHE will cause very few problems, even on a busy OLTP system. It will cause a small CPU spike for a few seconds as query plans get recompiled. It can be a useful tool when base-lining expensive queries or stored procedures.

If that’s not selective enough, you can free the cached plans for a single database using an undocumented DBCC command, FLUSHPROCINDB:

-- Flush all plans from the plan cache for a single database  

declare @dbid int;

select @dbid = dbid from master.dbo.sysdatabases where name = 'MyDatabaseName';



dbcc flushprocindb(@dbid);

If you want to remove a single plan from the cache:

-- Get the plan handle (varbinary(64)) for a cached query plan

select 

    cp.plan_handle, 

    st.text

from 

    sys.dm_exec_cached_plans cp 

    cross apply sys.dm_exec_sql_text(plan_handle) st

where 

    text LIKE N'%GetJournal%';



-- Remove a specific plan from the cache using its plan handle

dbcc freeproccache (0x060050000C267C1030CE4EC70300000001000000000000000000000000000000000000000000000000000000);

DBCC FREEPROCCACHE is not supported in SQL Azure as that wouldn’t be practical in a multi-tenanted database environment. SQL Azure (and SQL Server 2016) has introduced a new mechanism for clearing the query plans for a single database:

ALTER DATABASE SCOPED CONFIGURATION CLEAR PROCEDURE_CACHE;

ALTER DATABASE SCOPED CONFIGURATION

This statement enables the configuration of a number of database configuration settings at the individual database level, independent of these settings for any other database. This statement is available in both SQL Database V12 [SQL Azure] and in SQL Server 2016. These options are:

  • Clear procedure cache.

  • Set the MAXDOP parameter to an arbitrary value (1,2, …) for the primary database based on what works best for that particular database and set a different value (e.g. 0) for all secondary database used (e.g. for reporting queries).

  • Set the query optimizer cardinality estimation model independent of the database to compatibility level.

  • Enable or disable parameter sniffing at the database level.

  • Enable or disable query optimization hotfixes at the database level.

Database Scoped Configuration