Parameter Sniffing Primer

Parameter Sniffing Primer
4.5 (90%) 2 vote[s]

Introduction

Developers are often told to use stored procedures in order to avoid the so-called ad hoc queries which can result in unnecessary bloating of the plan cache. You see, when recurrent SQL code is written inconsistently or when there’s code that generates dynamic SQL on the fly, SQL Server has a tendency to create an execution plan for each individual execution. This may decrease overall performance by:

  1. Demanding a compilation phase for every code execution.

  2. Bloating the Plan Cache with too many plan handles that may not be reused.

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T-SQL Datetime Data Type

T-SQL Datetime Data Type
3.3 (66.67%) 3 vote[s]

Introduction

Data types are attributes that specify the kind of data that objects such as columns, local variables, expressions, and parameters can hold. Across the RDBMS world, data types are typically grouped into string, numeric, and date data types.

T-SQL supports 6 date and time data types namely:

  1. Datetime
  2. Smalldatetime
  3. Date
  4. Time
  5. Datetime2
  6. Datetimeoffset

The first two data types are considered as legacy versions of the newer ones. In this article, we focus on the date data types and, specifically, on the datetime and datetime2 data types available in SQL Server. Table 1 gives details of the various date and time data types available in SQL Server. Read More

Using Trace Flag 3226 to Suppress Log Backup Logging

Using Trace Flag 3226 to Suppress Log Backup Logging
3 (60%) 1 vote[s]

Introduction

Every backup operation in SQL Server is written to the SQL Server Error log. This includes Transaction Log Backups even when they occur as part of a Transaction Log Shipping Configuration. Sometimes logging the entire Log Backup can be a nuisance in the SQL Server Error Log and needs to be managed. Trace Flag 3226 is used to suppress such logging and we will demonstrate how this can be done in this article.

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Concatenation in Transact-SQL

Concatenation in Transact-SQL
3.5 (70%) 2 vote[s]

Introduction

Assuming you maintain a table containing customer data, and your boss asks you to send him the current list of customers and their phone numbers. You would typically extract the data and send him a spreadsheet with rows and columns. You could also decide to be a bit stylish and send him the required information in a more people-friendly format. SQL Server provides functions that allow us to achieve this by combining English expressions with data within tables to present an output that is easier for non-technical people to read. These functions can also be put to more subtle uses.

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In-depth Exploration of Row Level Security

In-depth Exploration of Row Level Security
4 (80%) 3 vote[s]

Introduction

Organizations are becoming more and more concerned about how to reduce the cost of licensing database solutions using consolidation. Some consolidation can be achieved in SQL Server simply by taking advantage of the existing one-to-many relationship between instances and databases. However, there are cases where the solution demands that data is consolidated into one table. In such a case, there may be concerns about how to restrict access to the data.

Row Level Security was introduced in SQL Server 2016 as a solution to scenarios similar to the above. It allows you to restrict access to rows in a table based on conditions defined in an inline Table Valued Function called a Predicate Function. When a Predicate Function is applied to a user table containing consolidated data, the system can be configured to return different data sets to different users depending on their roles which in turn depends on their job descriptions or departments for example.

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Dealing with NULLs in SQL Server

Dealing with NULLs in SQL Server
3.3 (66.67%) 3 vote[s]

What is NULL? NULL or the NULL marker is the way we represent an unknown value in SQL, by SQL I am referring to the standard Structured Query Language, not MS SQL Server. The last sentence takes us a little back to 1969 when the standard was first defined by Dr. E.F. Codd. NULL becomes necessary because we need to think in terms of what is called three-valued predicate logic. A predicate is the property of an expression that either holds or does not hold. At face value, one would think of two possibilities: TRUE or FALSE. However, there is a third possibility: UNKNOWN. Read More

Query Store: Showing the Impact of Indexes on Inserts

Query Store: Showing the Impact of Indexes on Inserts
4 (80%) 6 vote[s]

Introduction

It is common knowledge in database circles that indexes improve query performance either by satisfying the required result set entirely (Covering Indexes) or acting as lookups which easily direct the Query Engine to the exact location of the required data set. However, as experienced DBAs know, one should not be too enthusiastic about creating indexes in OLTP environments without understanding the nature of the workload. Using Query Store in SQL Server 2019 instance (Query Store was introduced in SQL Server 2016), it is quite easy to show the effect of an index on inserts. Read More

Navigating SQL Server Error Logs

Navigating SQL Server Error Logs
3.9 (77.14%) 7 vote[s]

Introduction

One of the key skills you need as a database administrator or an IT person is generally the ability to monitor systems very carefully. Lack of this key skill can lead to misdiagnosis when troubleshooting issues. SQL Server exposes a number of tools that can aid the DBA in troubleshooting problems that occur in production. The SQL Server Error Log and the SQL Server Agent Log are two of the most important facilities for troubleshooting SQL Server. In this article, we shall explore the ways we can manipulate the Server and Agent logs.

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Monitoring Backups Across Instances

Monitoring Backups Across Instances
3.8 (76%) 10 vote[s]

Introduction

In the last two or three months, I have been asked twice for a solution native to SQL Server that consolidates a backup report for several SQL Server instances across an enterprise. This question came from friends that did not necessarily want to spend money buying a tool but were more inclined to leverage the capabilities of SQL Server. I have thought about two possible ways to achieve this:

  1. Using Linked Servers, catalog views, SQL Agent Jobs and Database Mail
  2. Using Central Management Server

In this article, I will demonstrate the first and hope we shall have a second part of the article sometime later. Read More

Move Datafiles in SQL Server – Part 2

Move Datafiles in SQL Server – Part 2
3.9 (78.18%) 11 vote[s]

Introduction

In the first part of the two-part series, we explored migrating databases by first updating the master database system catalogs which contain records of the physical location of data files. In the current article, we shall look at two other methods of migrating databases in SQL Server which essentially have the same effect through the approach is different. Read More